Class VI Physics Simple Machines Notes and Questions

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VI - CLASS 50

PHYSICS SIMPLE MACHINES

LEARNING OBJECTIVES:

* Introduction

* Mechanical Advantage Ideal mechanical advantage (IMA),

Actual mechanical advantage (AMA).

* Types of simple Machines

Lever,Wheel and axle ,Pulley,Inclined plane,Wedge ,Screw

* Center of gravity:

* Location of Centre of gravity (CG)

* Determination of CG of irregular shape

* Stable equilibrium

* Unstable equilibrium

* Neutral equilibrium

Real life applications:

* Levers are used in door handles,the claws of hammer for removing nails, crowbars, light

switches, bottle openers and hinges.

* Wheels are used in an electric fan, a motor, a revolving door, a merry go round and any

wheel on the car, on your skate board, on a bicycle.

* pulleys are used in window blinds and drapery to move them up and down or back and forth,

on ships to raise and lower sails, in elevators to move the car up and down from floor to

floor, on cranes for use in moving construction equipment.

IMPORTANT FORMULE:-

1. Force Input

Force Output

MA  Effort(E)

Load(L)



2. IMA = R

3. AMA = actual E

4. M = Fd

5. Load x load arm = effort x effort arm

arm load

arm effort

MA   

6. Work done by load = work done by effort

M.A. = radius of wheel / radius of axle

SIMPLE MACHINES

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PHYSICS SIMPLE MACHINES

7. e plan Inclined of height

plane Inclined of length

  h

A M . .

8. M.A =length of the inclined surfaceof wedge / thickness of wedge

9. Px2  d = wxh

10. M.A. = 2  d/h

11. velocity ratio . displacement of the power

V R displacement of the load



12. .

Efficiency= .

M A

V R

13. .

P e rc e n ta g e o f E ffic ie n cy= 1 0 0

M A X

V R

Introduction

1. A simple machine is a mechanical device that changes the direction or magnitude of a force.

2. In general, they can be defined as the simplest mechanisms that use mechanical advantage

(also called leverage) to multiply force.

3. Simple machine uses a single app

The ratio of the output to the input force is called the mechanical advantage.

Force Input

Force Output

MA  Effort(E)

Load(L)



Here the force applied to a machine is called effort. The force overcome by a machine in

response to the effort is called load or resistance.

Types: There are two types of mechanical advantage, ideal mechanical advantage (IMA)

and actual mechanical advantage (AMA).

Ideal or perfect machine : A machine in which no part of the work done on the machine is

wasted,is called an ideal or perfect machine.thus for an idel machine work out put

=work input(efficiency is 1or 100%)

Ideal mechanical advantage: The ideal mechanical advantage (IMA), or theoretical me-

chanical advantage, is the mechanical advantage of an ideal machine. It is calculated

using physics principles because no ideal machine actually exists.

The IMA of a machine can be found with the following formula: IMA = R

where DE equals the ‘effort distance’ (for a lever, the distance from the fulcrum to where the

effort is applied)

DR equals the load distance (for a lever, the distance from the fulcrum to where the resis-

tance is encountered)

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PHYSICS SIMPLE MACHINES

Actual mechanical advantage: The actual mechanical advantage (AMA) is the mechanical advan-

tage of a real . Actual mechanical advantage takes into consideration real world factors such

as energy lost in friction.

The AMA of a machine is calculated with the following formula:AMA = actual E

where R = resistance force obtained from the machine,

Eactual = actual effort force applied to the machine

Types of simple Machines

Usually Simple machines refers to the six classical simple machines which are

1. Lever , 2.Wheel and axle , 3 Pulley 4. Inclined plane , 5. Wedge , 6.

Screw

Simple machines fall into two classes; those dependent on the vector resolution of

forces (inclined plane, wedge, screw) and those in which there is an equilibrium of

torques (lever, pulley, wheel).

1. LEVER :

In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to

multiply the mechanical force (effort) that can be applied to another object (load). A lever is

one of the six simple machines.

1. “Give me a place to stand, and I shall move the earth with a lever”

is a remark of Archimedes.

2. It is assumed that in ancient Egypt, constructors used the lever

to move and uplift obelisks weighting more than 100 tons.

Force and levers

1. The force applied (at end points of the lever) is proportional to the ratio of the length of the

lever arm measured between the fulcrum (pivoting point) and application point of the force

applied at each end of the lever.

2. Mathematically, this is expressed by M = Fd, where F is the force, d is the distance between

the force and the fulcrum, and M is the turning force known as the moment or torque.

Classes of Levers

There are three classes of levers representing variations in the relative locations of the fulcrum, the

load and the force.

Class 1: The fulcrum is located between the applied force and the load. Example:

Crowbar pair of scissors seesaw

The below figure shows a class 1 lever under equilibrium. The fulcrum acts at point ‘O’

such that Load x load arm = effort x effort arm

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PHYSICS SIMPLE MACHINES

that is L x ON = E x MO NO

L   arm load

arm effort

MA   

M O N

F u lc r u m

Thus, the mechanical advantage of a lever depends on the ratio of the lenghts of the

effort arm to the load arm.

Class 2: The load is situated between the fulcrum and the force.

In class 2 levers, the effort arm is always greater than the load arm. Therfore the M.A. is

always greater than one. Thus by using a class 2 lever, a greater load can be lifted with

a lesser effort i.e., class 2 levers are used as force multipliers.

Class 3: The force is applied between the fulcrum and the load. Examples

Brooms stick Tongs Fishing Rod

In class 3 levers, the length of load arm is always greater than that of effort arm.

Therfore the M.A. is always less than one. Hence it can not be used as force multiplier.

Insted class 3 levers are used as speed multipliers.

Class 1 Lever Class 2 Lever Class 3 Lever

Example 1: A construction worker uses a board and log as

a lever to lift a heavy rock. If the input arm is 3 meters

long and the output arm is 0.75 meterslong, what is

the mechanical advantage of the lever?

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PHYSICS SIMPLE MACHINES

Solution:

3 m

M.A. 4

0.75 m

input arm length

output arm length

  

Example 2: The mechanical advantage of a mechine is 4 and its velocity ratio is 5. what is its

percentage efficiency?

Solution .

Percentage of Efficiency= 100

M A X

V R

Efficiency= .

M A

V R 4

Efficiency= 0.8

5 

80% percentage of efficency  

Example 3: A machine is operated by a power of 50 N and the power has a downward

displacement of 0.25 m in raising a load of mass 100N through 10 cm. calculate M.A.,

V.R. and efficiency.

Solution:

Load(L) 100

. Effort(E) 50

Load

M A power

  

M.A=2

. displacement of the power

V R displacement of the load



0.25

. 2.5

0.1

V R  

. 2

Efficiency= 0.8

. 2.5

M A

V R  

Example 4: A lever used to lift a heavy box has an input arm of 24 meters and an output arm

of 6 meters. What is the mechanical advantage of the lever?

Solution:

M.A. 4

input arm length

output arm length

  

Example 5: The mechanical advantage of a liver is 2. load applied by the person on liver is

20N.what is the effort on it?

Solution :

Load(L)

. Effort(E)

Load 20 10

. 2

M A

Effort N

M A



  

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PHYSICS SIMPLE MACHINES

I. Single Correct Answer Type:

1. The mechanical advantage of machine is 5 and its efficiency is 80% it is used with a

load 200kgf to height of 20m .calculate the effect required ?

A) 40kgf B) 80kgf C) 95kgf D) 10kgf

2. A lever is used to lift a heavy box has an input arm of 4m and an output arm of 0.8m what is

the mechanical advantage ?

A) 4 B) 0.4 C) 5 D) 0.2

3. What is the mechanical advantage of lever that has an input arm of 3m and an output on

arm’s lenth is 2m

A) 1.5 B) 0.4 C) 2 D) 0.2

4. A lever is held so that its input arm is 0.4 meters and its output arm is 1.0 meters. What is

the mechanical advantage of the lever?

A) 4 B) 0.4 C) 2 D) 0.2

5. A broom with an input arm length of 0.4 meters has a mechanical advantage of 0.5. What is

the length of the output arm?

A)8 B)20 C)2 D)0.8

6. A child’s toy is held so that its output arm is 0.7 meter. If the mechanical advantage is 0.3,

what is the input arm length?

A)1.8 B) 0.21 C) 0.42 D) none

7. A crow bar ,of length 120cm as fulcrum situatued at a distance of 20cm from theload calcu-

late the mechanical advantge of the crowbar?

A) 2.2 B) 5 C) 0.85 D) 3.4

8. A boy ’s toy rake is held so that its output arm is 90 meters. If the mechanical advantage is

0.30, what is the input arm length?

A)27 B) 27.5 C) 37 D) 300

9. If 20m is the displacement caused by an effort in the time t ,such that 5m is thedisplacment

caused by the load in the same time then velocity ratio is ?

A)100 B) 40 C) 4 D) 1/4

10. Agirl’s toy with the lenth of its output arm is 20 meters. If the mechanical advantage is 0.5,

what is the input arm length?

A)100 B) 40 C) 4 D) 10

Multiple option type:

11. Simple machines is dependent on in these vector resolution of forces

a)inclined plane b) wedge c) screw d) lever

A) a, b correct B) b , c correct C) a , b , c correct D) b , c , d correct

12. The M.A. is always less than one in case of

a)Crowbar b) Tongs c) Pair of scissors d) Fishing rod

A) a, b correct B) b , c correct C) a , b , c correct D) b , d correct

TEACHING TASK

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PHYSICS SIMPLE MACHINES

Fill in the blanks:

13. The ratio of the output to the input force is called ................

14. The IMA of a machine can be found with the ,....................

15. ................. is a rigid object that is used with an appropriate fulcrum to multiply

themechanical force applied to another object .

16. The length of load arm is always greater than that of effort arm. then the M.A. is .......

17. The effort arm length is always greater than the load arm length .then the M.A. is

...............

Assertion - A and Reason - R:

A) Both A and R are true and R is correct explanation of A

B) Both A and R are true and R is not correct explanation of A

C) A is true but R is false D)A is false but R is true

18. A: In class 3 levers,the length of load arm is always greater than that of effort arm

R:class 3 levers are used as speed multipliers.

19. A: In class 2 levers,the length of load arm is always greater than that of effort arm

R:class 2 levers are used as force multipliers.

Match the following:

20. Column A Column B

A. Human fore arm 1. MA

B. Load/effort 2. 3 rd class lever

C. Bread knife 3. 1 st class lever

D. Chistel 4. 2 nd class lever

A) A-3, B-4, C-1 D-2 B)A-4, B-3, C-2, D-1

C) A-3, B-1 C-2, D-4 D) A-3, B-2, C-4, D-1

Comprehention type:

21. A construction worker uses a board and log as a lever to lift a heavy rock. If the input arm is 4

meters long and the output arm is 0.5 meter slong

i) which type of lever they are used?

A) Class 1 lever B) Class 2 lever C) Class 3 lever D) none

ii) what is the mechanical advantage of the lever?

A) 2 B) 4 C) 6 D) 8

Key:-1) A, 2) C, 3) A , 4) B, 5) D, 6) B, 7) B,8) A , 9)C, 10) D 11) C, 12) D, 13) The mechani-

cal advantage , 14) IMA = / E R D D ,15) a lever, 16) always less than one, 17) always

greater than one, 18) A, 19) D, 20) C, 21) i) A , ii) D

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PHYSICS SIMPLE MACHINES

Choose the correct option:

1. The stair case used by the airline passengers is a modified form of

A) lever B) Wedge C) inclined plane D) pulley

2. In the first order lever, by keeping the load constant the effort decreases if

A) the fulcrum is moved towards the load

B) the fulcrum is moved away from the load

C) the fulcrum is moved towards the effort

D) Both B and C

3. Which of the following are correct examples of first, second and third class levers?

First class Lever Second class Lever Third class Lever

I Scissors Wheel Barrow Broom

II Ice tongs Tweezer Paper cutter

III Pliers Nut cracker Fishing rod

A) I and II only B) II and III only C) III and I only D) I, II and III

4. Choose the correct inthe case of hammer and nut cracker

I. Both are simple machines

II. Both are second class levers

III. Both have a fulcrum between load and force

A) I and II only B) II and III only C) I and III only D) I, II and III

5. Table shows the weights of three students sitting on see-saw.

Student Razali Ayu Kamela

Weight 800 N 400 N 400 N

1 m 1.5 m

Razali Kamela

1 m 2 m

Ayu Razali

2 m 1.5 m

Ayu Kamela

1 m 2 m

Razali Ayu

LEARNER’S TASK

BEGINNERS ( Level - I )

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PHYSICS SIMPLE MACHINES

6. Which of the following levers are in equilibrium?

2 N

2 m 0.03 m

0.2 kg

2 N

2 m 0.05 m

3 N

0.2 kg

3 m 1 m

2 N

0.4 kg

2 m 2 m

2 N

7. Which is not simple machine?

A)switches B) a drill C) screw D)scissors

8. Which is not first order lever?

A)switches B) scissors C) screw D) bicycle

9. Write a relation expression of the mechanical advantge of a lever ?

A) effortarm

loadarm B)effort arm X load arm C) loadarm

effortarm D) none

10. the ratio between work output and work input is called......?

A) Fulcrum B)efficiency C)MA D) none

11. velocity ratio is........

A) velocityofeffort

velocityofload B) effortarm

loadarm C) MA D) none

Multiple option type:

12. Levers are used in

a)switches b) a drill c) bottle openers d) escalators

A) a, b correct B) a , c correct C) a , b , c correct D) b , c , d correct

13. Mechanical advantage = ..........................

a) MA= Fd, b) load by effort c) MA = actual E

R d) Effortarm

MA Loadarm



A) a, b correct B) a , c correct C) a , b , c correct D) b , c , d correct

Fill in the blanks:

14. A wheel barrow is an example of .........................

ACHIEVERS ( Level - II )

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PHYSICS SIMPLE MACHINES

15. In a second order lever, the effort arm is always ...................... than load arm.

16. Third class levers acts as .................... multipliers

17. A bottle opener is an example of ........................

Assertion - A and Reason - R:

A) Both A and R are true and R is correct explanation of A

B) Both A and R are true and R is not correct explanation of A

C) A is true but R is false D)A is false but R is true

18. A: The force is applied between the fulcrum and the load in third class lever

R: the load acts in the middle of effort and fulcsurm in third class lever.

19. A: length of effort arm of meter scale is 75cm and length of load arm meter scale is

25cm then its MA=3

R: M.A.  input arm length

output arm length

Match the following:

20 Column A Column B

a) Work done on the machine by effort 1) Effort

b) Force applied on the machine to overcome the load 2) Mechanical advantage

c) Ratio of load to effort 3) Work input

d) Work done by the machine on the load 4) work output

A) a-3,b-4,c-1,d-2 B) a-3,b-1,c-2,d-4 C) a-3,b-4,c-2,d-1 D) a-3,b-2,c-4,d-1

Comprehention type:

21. Sometimes levers are used to multiply distance. For a broom, your upper hand is the ful-

crum and your lower hand provides the input force in 0.5 m long and the load arm is 2 meter.

i) which type of lever they are used?

A) Class 1 lever B) Class 2 lever C) Class 3 lever D) none

ii) what is the mechanical advantage of the broom?

A) 0.25 B) 4 C)1 D) 8

22. A lever used to lift a heavy box has an input arm of 0.4 meters and an output arm of 4

meters. What is the mechanical advantage of the lever? (Ans:0.1)

23. What is the mechanical advantage of a lever that has an input arm of 4.8 meters and an

output arm of 2 meters? (Ans:2.4)

24. A lever with an input arm of 2.5 meters has a mechanical advantage of 2. What is the output

arm’s length? (Ans:1.25)

25. A lever with an output arm of 1.2 meter has a mechanical advantage of 4. What is the length

of the input arm? (Ans:4.8)

Level -4

EXPLORERS ( Level - III )

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PHYSICS SIMPLE MACHINES

26. A rake is held so that its input arm is 1.5 meters and its output arm is 3.0 meters. What is

the mechanical advantage of the rake? (Ans:0.5)

27. A broom with an input arm length of 1.4 meters has a mechanical advantage of 0.2. What is

the length of the output arm? (Ans:7)

28. A child’s toy rake is held so that its output arm is 1.7 meters. If the mechanical advantage is

0.5, what is the input arm length? (Ans:0.85)

Key:-1 - C , 2 - A , 3 - C , 4 - B , 5 - D , 6 - D , 7 - B ,8 -D,9- A,10 - B , 11-A 12-B 13-D 14- 2 nd

order lever , 15-greater, 16- Speed , 17- second order lever , - 18 - C, 19 - A 20.B 21)

i - C, ii - A

2. Wheel and axle: It is a simple machine and is used to lift heavy loads. It has a wheel of

larger radius (R) and an axle of smaller radius (r) fixed on the same shaft. Wheel and

axle are free to rotate about its shaft.

Mechanical Advantage : The effort is applied to the rim of the wheel and the load is

raised by a rope wound around the axle. In one rotation wheel covers a distance of 2 π R In

one rotation load is raised by a distance of 2 π r If we neglect force of friction, Work done

by load = work done by effort

L x 2 π r = E x 2 π R r

r 2

R 2

L     π

π .

M.A. M.A.

since  









 

M.A. = radius of wheel / radius of axle

This expression indicates that in order to increase the mechanical advantage Radius

of wheel must have a large value, radius of axle must be smaller than that of wheel.

In villages wheel and axle is used for lifting water from a well. This form consists of a wheel

that turns an axle, which turns a rope, which converts the rotational motion to linear motion

for the purpose of lifting.

Examples: Gears, Bicycle wheels, Ferris wheels , automobiles, blenders, clocks, escalators,

golf carts, helicopters, jet, lawn mowers, microwaves, propellers.

3. Pulley: A pulley is a simple machine. It consists of a wheel mounted on an axis which is

fixed to a frame called block. The wheel is free to rotate. With the help of pulley we can

lift heavy loads very easily by applying little force and also change the direction of force.

Types of Pulleys:

a) Fixed Pulley: If the block of the pulley is fixed to a strong beam

or ceiling, the pulley will not move and is called a “Fixed Pulley”.

Mechanical Advantage: In fixed pulley, the effort ‘E’ is applied

which is equal to the load ‘L’, if we ignore weight of rope

and force of friction between rope and pulley then :

effort = load that is E = L (or) L/E = 1,

Hence M.A = 1 This shows that fixed pulley can only change the direction of force but it will

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PHYSICS SIMPLE MACHINES

lift load equal to the effort applied on it.

b) Movable Pulley: In a moveable pulley, one end of the rope which passes

around the pulley is tied to a firm support ‘O’ and effort ‘P’ is applied

to the other end. The load is hung from the hook of the block. As the

load is applied by two segments of rope, the effort becomes twice

of the applied value i.e.

Mechanical Advantage: In equilibrium condition we have

Load = Effort, L = 2E that is L/E = 2

Hence M.A. = 2 This shows that a moveable pulley can lift a load double the effort.

c) Compound Pulley: A compound pulley is a combination of a fixed and a movable pulley

system.

4. Inclined Plane:Any smooth plane surface which makes an angle q with the horizontal

surface is called an “Inclined plane”. Where 0o < q <90o or values of q lies between 0o

and 90o .

Mechanical Advantage: In the figure AB is an inclined plane which makes an angle

 with

the horizontal plane. A load ‘L’ is being raised from A to B by applying an effort ‘E’. If we

neglect the force of friction between load and inclined plane

Work done by load = Work done by effort

 Weight x height = effort x distance

L x h = E x l h

L  

e plan Inclined of height

plane Inclined of length

  h

A M . .

Use: It is a simple machine and is used to raise heavy loads by applying little effort.

5. Wedge:

Wedge is also a type of simple machines. It is used in levers as

a fulcrum. It is also used for splitting the wood in to small

pieces. It is used as an Axe.

A wedge is made of two inclined planes joined together. The effort ‘P’ is applied on the top of

the wedge placed over a wood log. The wedge enters the wood and splits it. The reaction

forces R1 & R2 are acting perpendicular on the inclined planes of the wedge. These forces

and resultant frictional forces are responsible for keeping the wedge inside the wood firmly.

Mechanical Advantage: Let us consider that the wedge is in equilibrium under the

action of forces three forces R1, P and R2 and neglecting frictional forces. According to figure

below the forces P, R1 and R2 are represented by the sides of XYZ such that effort P the

reaction R1 and R2 are represented by XY, YZ, ZX which are the sides of XYZ respectively.

For equal sides of wedge i.e. = R1 = R2 = R

M.A. = R/P

M.A = ZX/XY Triangle ABC and triangle XYZ

are similar, therefore, ZX=AC and XY=BC

M.A. = AC/BC

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PHYSICS SIMPLE MACHINES

Mechanical advantage = length of inclined surface of wedge/thickness of wedge From above

expression it is clear that if the thickness of the wedge is decreased the mechanical advan-

tage of the wedge will increase & if the wedge is more sharper , then the mechanical advan-

tage will increase.

6) Screw:

Screw is one of the most important machines. It is used to hold different parts of machines

together. It has vast applications in our daily life plus in industries. It is used in every type of

device.

It simply consists of a threaded rod with a head known as “Screw head”. It has a number of

threads. The perpendicular distance between two adjacent threads is known as pitch

of screw. The thread of screw can be regarded as a continuous inclined plane wrapped

round a cylinder of radius d .

Mechanical Advantage: If we apply an effort ‘P’ on the head of screw then it turns one

revolution and at the same time the screw moves forward in to the wood or wall through a

distance equal to its pitch “h”. The effort ‘P’ moves through a distance 2 π d. The screw

remains in the wood due to frictional forces between the screw and the wood. A large amount

of energy changes in to heat energy during the process of screwing.

Let us assume an ideal case when there is no loss of energy then;in this condition

Output = input that is P x 2  d = W x h (or) W/P = 2  d/h

Hence, the mechanical advantage of the screw will be. M.A. = 2  d/h

The mechanical advantage of the screw depends upon the following

factors.

PITCH: In order to increase mechanical advantage of screw we must use a screw

of small pitch.

RADIUS OF SCREW: Larger is the radius of screw head, greater is the mechanical advantage.

Center of gravity:

Center of gravity of body is defined as a point of application of the resultant force due to the

earth’s attraction on it.

1. The center of gravity is a geometric property of any object.

2. The center of gravity is the average location of the weight of an object.

3. We can completely describe the motion of any object through space in terms of the transla-

tion of the center of gravity of the object from one place to another, and the rotation of the

object about its center of gravity if it is free to rotate.

4. A kite, on the other hand, rotates about the bridle point. But the trim of a kite still depends on

the location of the center of gravity relative to the bridle point,because for every object the

weight always acts through the center of gravity.

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PHYSICS SIMPLE MACHINES

Location of Centre of gravity (CG):

The centre of gravity of some objects are given below in table below

Determination of CG of irregular shape:

Aim : To determine the centre of gravity of an irregularly shaped lamina using a plumb line.

Procedure :

1. Make three holes near the edge of the lamina so that the lamina swings freely when pivoted

from each hole.

2. Hang the lamina about one of its holes on a pin clamped on a retard stand.

3. Suspend a plumb line from P and mark the position PP' on the lamina.

4. Repeat the experiment by suspending the lamina from Q and R and similarly mark the

plumb line positions QQ' and RR'.

5. All the three lines, PP', QQ' and RR' intersect at one point. This point of intersection of these

lines is the centre of gravity of the lamina.

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PHYSICS SIMPLE MACHINES

Stable equilibrium: A body is said to be in stable equilibrium, if it regains its original position when

slightly disturbed.

Ex: 1) a bottle standing on its base

2) a cone lying on its base

3) funnel resting on its mouth.

Unstable equilibrium: If body does not regain its original position after being slightly disturbed, the

equilibrium is said to be unstable.

Ex: 1) a bottle is standing on its mouth

2) a cone is erect on its vertex

3) a funnel perched on its stem.

Neutral equilibrium: If, after being slightly disturbed, a body changes its position without change in

equilibrium, the equilibrium is said to be neutral.

Ex: 1) a bottle lying on its side

2) a cone lying on its curved surface

3) a funnel lying on its side.

Example 1: To pull a weed out of a garden, you can apply a force of 20 N to the shovel. The

shovel applies a force of 180 N to the weed. What is the mechanical advantage of the

shovel?

solution:

O utp u t F orce 1 8 0

M .A 9

In p u t F o rce 2 0

  

Example 2: To lift a refrigerator, you can apply a force of 20 N to the wedge. The wedge

applies a force of 180 N to the weed. What is the mechanical advantage of the wedge?

Solution :

Output Force 180

M.A 9

Input Force 20

  

Example 3: A brick has is dimensions 36 cm x 24 cm x 6 cm. Find the ratio of its heights of

centres of gravity, when it have maximum stability and minimum stability

Solution : lowest height of the Brick gives maximum stability.

i.e, lowest height of the Brick=6cm

height of centre of gravityhMax=6cm/2=3cm

heighest height of the Brick gives minimum stability.

i.e,heighest height of the Brick=36cm

height of centre of gravityhmin=36cm/2=18cm.

The ratio of its heights of centres of gravity=3cm:18cm =1:6

Example 4: A cylinder of height 14 cm and diameter 4 cm. The decrease in height of its C.G

when its position is changed

Solution: minimum height of C.G=4cm/2=2cm

EXAMPLES

VI - CLASS 65

PHYSICS SIMPLE MACHINES

Example 5: In the diagram shown below. The resistance (R)

offered by the nut when an effort of 30N is applied.

5cm

20cm

nut

E = 30N

Solution: Load x load arm = effort x effort arm

loadx5cm=30Nx25cm

load=150N

The resistance (R) offered by the nut=150N

Choose the correct option:

1. To pull a weed out of a garden, you can apply a force of 50 N to the shovel. The shovel

applies a force of 600 N to the weed. What is the mechanical advantage of the shovel?

A) 12 B) 10 C) 8 D) 15

2. To pry a nail out of a wall, you can apply a force of 50 N to the hammer. The hammer applies

a force of 650 N to the nail. What is the mechanical advantage of the hammer?

A) 15 B) 10 C) 13 D) 11

3. To lift a block on a movable pulley, you can apply a force of 50 N to a rope. The rope applies

a force of 700 N to the block. What is the mechanical advantage of the rope?

A) 18 B) 10 C) 16 D) 14

4. To pull apart two pieces of wood, you can apply a force of 50 N to the lever. The lever applies

a force of 650 N to the weed. What is the mechanical advantage of the lever?

A) 15 B) 13 C) 17 D) 11

5. To lift a refrigerator, you can apply a force of 50 N to the wedge. The wedge applies a force of

550 N to the weed. What is the mechanical advantage of the wedge?

A) 18 B) 9 C) 13 D) 11

6. To pry open a sodacan lid, you can apply a force of 50 N to a car key. The car key applies a

force of 390 N to the lid. What is the mechanical advantage of the car key?

A) 6 B) 8 C) 10 D) 12

7. To lift a bookshelf, you can apply a force of 50 N to a wedge. The wedge applies a force of

800 N to the bookshelf. What is the mechanical advantage of the wedge?

A) 20 B) 18 C) 16 D) 22

8. To pry a wooden board off of a treehouse, you can apply a force of 50 N to a lever. The lever

applies a force of 750 N to the weed. What is the mechanical advantage of the lever?

A) 15 B) 18 C) 12 D) 13

9. To lift a television, you can apply a force of 50 N to a wedge. The wedge applies a force of

480 N to the weed. What is the mechanical advantage of the wedge?

A) 12 B) 10 C) 15 D) 22

10. To pull a tree out of a yard, you can apply a force of 50 N to the shovel. The shovel applies a

force of 900 N to the weed. What is the mechanical advantage of the shovel?

A) 20 B) 12 C) 18 D) 16

TEACHING TASK-2

VI - CLASS 66

PHYSICS SIMPLE MACHINES

11. Based on the figure what could be the force P and Q?

I. P=3 N, Q=6 N

II. P=6 N, Q=12 N P Q

6 m 3 m

III. P= 9 N, Q=15 N

A) I and II only B) II and III only

C) I and III onlyD) I, II and IIII

12. Calculate the value of X in the figure given below

A) 140 N B) 105 N

35 N

5 cm 15 cm

C) 99 N D) 70 N

13. The diagram shows a lever in action.

Where is the fulcrum of the lever?

A) P B) Q C) R D) S

14. Which of the following are first class levers

I. Wheel Barrow II. Pliers III. Scissors

A) I and II only B) I and III only C) II and III only D) I, II and III

15. S

Which of the following matches its Load (L), Ful crum (F)

and effort (E) correctly? For the figure shown

L F E

A) P Q S

B) P R S

C) Q P S

D) Q P R

16. If a person siting in a cradle stands up

A) CG moves up B) CG moves down

C) No change in the position of CG D) may or may not change depending of person

Multiple option type:

17. A screw is preferred over a nail to insert into wood because

a) screw holds more firmly than a nail b) Less force is needed to insert a screw

c) tip of a screw has more area of contact than nail

d) fulcrum, of the screw is at its head

A) a, b correct B) b , c correct C) a , b , d correct D) b , c , d correct

18. A simple mechine is a device that makes work easier by

a) multiplying force b) multiplying speed

c) applying force at a convenient point d) applying force in a convenient direction

A) a, b correct B) b , c correct C) a , b , d correct D) a, b , c , d correct

VI - CLASS 67

PHYSICS SIMPLE MACHINES

19. The effort moves through a larger distane than the load by applying a small force. identify the

example of devices from the following using the type of lever described.

A) pliers B) diving board C) nut cracker D) ice tongs

A) a, b ,c correct B) b , c correct C) a , b , d correct D)a, b , c , d correct

Fill in the blanks:

20. ..................... is used to seperate two objects into pieces.

21. A flat plank can be used as an ..........................

22. ........................ is used to pull water from a well.

23. An external force applied to a simple machine to over come the load is .................

24. An egg beater is an example of ...........................

Assertion - A and Reason - R:

A) Both A and R are true and R is correct explanation of A

B) Both A and R are true and R is not correct explanation of A

C) A is true but R is false D)A is false but R is true

25. A: Mechanical advantge of wheel is the ratio of radius of wheel to radius of axle

R:radius of wheel 2

 r

26. A: by moving the fulcurm towards load, the the mechanical advantge can be increased

R: by keeping load constant.

Match the following:

27. Column A Column B

A. Wheel and axle 1. Nut and bolt

B. Inclined Plane 2. Axe

C. Screw 3. Door knob

D. Wedge 4. Ramp A)

a-3, b-4, c-1 d-2 B) a-3, b-1, c-2, d-4

C) a-3, b-4, c-2, d-1 D) a-3, b-2, c-4, d-1

Comprehention type:

28 A simple machine is used to lift heavy load 50 N. It has a wheel of larger radius (R = 21 cm)

and an axle of smaller radius (r = 14 cm ) fixed on the same shaft. Wheel and axle are free

to rotate about its shaft. Work done by load = work done by effort

i) The work done by load is

A) 44 J B) 22 J C) 66 J D) 33 J

ii) what is the mechanical advantage of the wheel?

A) 15 B) 1.5 C) 0.66 D) 6.6

Key: 1) A , 2) C , 3) D, 4) B, 5) D, 6) B, 7) C, 8) A , 9) B, 10) C, 11) A , 12) A , 13) C, 14) C, 15) C, 16)

A , 17) C, 18) D, 19) A, 20) wedge, 21) inclined plane, 22) wheel and axle, 23) effort, 24) third

order lever, 25) C, 26) A, 27) A, 28) i) A, ii) B

VI - CLASS 68

PHYSICS SIMPLE MACHINES

Choose the correct option:

1. Where does the center of gravity of the atmosphere of the earth lie?

A) at geometric centre of earth B) at north pole

C) at south pole D) on equator of earth

2. A road roller is in

A) stable equilibrium B) unstable equilibrium

C) Neutral equilibrium D) none of the above

3. If water leaks out from a hole at the bottom of a hallow sphere full of water then

A) CG shifts downwards B) CG moves upwards

C) no change in the position of CG

D) CG first shifts downwards then rises up to original position

4. The CG of uniform circular lamina and CG of an annular ring of same radius

A) coincide B) do not coincide C) may or may not coincide D) can’t say

5. The CG of a regular cuboid is

A) at the centre of the large face B) at the centre of a small face

C) at one of the corners D) at the point of intersection of body diagonals

6. Where will be CG of a triangle lies

A) at one of the vertex B) at centroid C) at mid point of its one of the side D) none

7. As the inclination of the screw increases, the distance between the threads

A) increases B) decreases C) remains the same D) may increase or decrease

8. Distance between two succsive threads of a screw is called

A) arm length B) principle of screw C) pitch of screw D) least count

9. Example of wheel and axle is

A) egg beaters B) egg whiskers C) clocks D) electric saw

10. Screw is a/an

A) lever B) gear C) inclined plane D) wheel

11. Modified inclined plane is a

A) lever B) wheel C) screw D) axle

12. mechanical advantage of wheel and axle is (R = radius of the wheel, r = radius of the

axle

A) R + r B) R/r C) r/R D) R - r

LEARNER’S TASK

BEGINNERS ( Level - I )

VI - CLASS 69

PHYSICS SIMPLE MACHINES

Multiple option type:

13. Which of the following statements is correct ?

a) In a first order lever, the fulcrum is placed between the effort and the load

b) The mechanical advantage of a second class levers is greater than 1 as load is

situated in between to effort and fulcrum

c) An inclined plane in a hospital, helps in pushing a wheel chair easily

d) A crow bar is an example of second class lever

A) a, b correct B) b , c correct C) a , b , d correct D) a, b , c , correct

14. Which of the follwing devices have the fulcrum between the load and the effort ?

a) seaSaw b) Screw c) Scissors d) Crane

A) a, b correct B) b , c correct C) a ,c correct D)a , c , d correct

15. Which of these devices have the load between the fulcrum and effort ?

a) nut cutter b) Scissors c) fishing rod d) wheel barrow

A) a, b correct B) b , c correct C) a , d correct D)a, b , c , d correct

Fill in the blanks:

16. In villages ---------- is used for lifting water from a well.

17. A pulley consists of a wheel mounted on an axis which is fixed to a frame is called ---

18. ........... is used for splitting the wood in to small pieces

Assertion - A and Reason - R:

A) Both A and R are true and R is correct explanation of A

B) Both A and R are true and R is not correct explanation of A

C) A is true but R is false D)A is false but R is true

19. A: fulcurm is in between load and effort in class 1 lever

R: fulcurm is used find the mechinical advantge

20. A: by moveing the fulcurm towards load, the the mechanical advantge can be increased

R: Length of the effort arm is increased

Match the following:

21. Column A Column B

a. Wheel and axle 1. M.A = 1

b. Fixed Pulley 2. length of inclined surface

M.A = thickness

c. Movable Pulley 3.M.A. = 2

d. Wedge 4. M.A. = radius of wheel / radius of axle

A) a-3, b-4, c-1 d-2 B) a-3, b-1, c-2, d-4 C) a-3, b-4, c-2, d-1 D) a-4, b-1, c-3, d-2

ACHIEVERS ( Level - II )

VI - CLASS 70

PHYSICS SIMPLE MACHINES

Comprehention type:

22. In the figure AB is an inclined plane which makes an angle 45o with the horizontal

oad is 40 N being raised from A to B by applying an effort ‘E’. If we neglect

the force of friction between load and

inclined plane, AB=2 m

i) Find the height of the incined plane OB

A) 2 m B) 4 m C) 1 m D) 6 m

ii) what is the mechanical advantage of the inclined plane?

A) 2 B) 4 C) 2 D) 6

Key: 1) A, 2) C, 3) D, 4) A, 5) D, 6) B, 7) B, 8) C, 9) C, 10) C, 11) C, 12) B, 13) D, 14) C, 15) C,16)

wheel and axle, 17) block, 18) Wedge 19) A , 20) A, 21) D, 22) i)A , ii) C

1. The distance of CG from one of the corner of a lamina in the form of a square of length 10

cm is

A) 5 2 cm B) 2 cm D) 10 cm D) 5 cm

2. A brick has is dimensions 16 cm x 8 cm x 4 cm. Find the ratio of its base areas , when it has

maximum stability and minimum stability

A) 4 : 1 B) 1 : 4 C) 1 : 2 D) 2 : 1

3. A brick has is dimensions 16 cm x 8 cm x 4 cm. Find the ratio of its heights of

centres of gravity, when it have maximum stability and minimum stability

A) 1 : 4 B) 2 : 3 C) 1 : 2 D) 2 : 1

4. A cylinder of height 12 cm and diameter 5 cm. The decrease in height of its

CG when its position is changed

A) 6 cm B) 3.5 cm C) 2.5 cm D) 2 cm

Key: 1) A, 2) A, 3) A ,4) C,

Archieves:

1. A screw is essentially a lan:

A) wheel and axle B) lever C) pulley D) inclined plane

2. The pulley and lever uses mechanical energy to move an object.The pulley and lever

are examples of [NSO-2010]

A) circuits B) magnets C) measurement tools D) simple machines

EXPLORERS ( Level - III )

RESEARCHERS ( Level - IV )