Question Bank

Std 10

Physics

Chapter I

Force

Unit 1:-

1. State the conditions when on applying a force the body has:

(a) The Translational motion

(b) The Rotational motion.

Ans.

(a) When the body is free to move.

(b) When the body is pivoted at a point.

2. Define Moment of Force and state its S.I. unit.

Ans.

The Moment of Force or Torque is equal to the product of the magnitude

of force and the perpendicular distance of the line of action of force

from the axis of rotation.

3. State whether the moment of force is a SCALAR or VECTOR

quantity.

Ans.

The moment of force is a VECTOR quantity.

4. State two factors affecting the turning effect of a force.

Ans.

The magnitude of force

The perpendicular distance of the line of action of force from the

axis of rotation.

5. When does a body rotate? State one way to change the direction of

rotation of the body. Give a suitable example to explain your answer.

Ans.

A body will rotate if it is fixed on a pivot and a force is applied at some

point on the body.

The direction of rotation of the body can be changed by changing the

direction of the force applied on the body.

6. Write the expression for the moment of force about a given axis.

Ans.

Moment of force = force * the perpendicular distance of the line of

action of force from the axis of rotation.

7. What do you understand by the clockwise and anti-clockwise

moment of force? When is it taken positive?

Ans.

If the effect of the force on the body, is to turn it anti-clockwise then it

is called anticlockwise moment of force, and if the effect on the body

turns it clockwise then it is called clockwise moment of force.

The anticlockwise moment of force is said to be positive

8. State one way to reduce the moment of a given force.

Ans.

The moment of force can be reduced by reducing the perpendicular

distance of the line of action of force to the axis of rotation.

9. State one way to obtain a greater moment of force about a given

axis of rotation.

Ans.

The moment of force about a given axis of rotation can be increased by

increasing the perpendicular distance of the line of action of force form

the axis of rotation.

10. Why is it easier to open a door by applying a force at the free

end of it?

Ans.

It is easier to open a door by applying the force at the free end of it

because when we apply the force at the free end of a door, we are

essentially applying a force at a larger perpendicular distance from the

axis of rotation (in this case the hinge of the door) and as the moment

of force increases with the with the increase in the perpendicular

distance, so, it would take less amount of force to open the door and

the door can be opened easily.

11. The stone of a hand floor grinder is provided with a handle

near its rim. Give reason.

Ans.

The stone of a hand floor grinder is provided with a handle near its rim

so as to increase the perpendicular distance from the axis of rotation

and in a result increase the turning effect of the grinder making it easy

to grind wheat with a less amount of force applied.

12. It is easier to turn the steering wheel of a large diameter than

that of a small diameter. Give reason.

Ans.

It is easier to turn a steering wheel of large diameter than the steering

wheel of short diameter because in a steering wheel of large diameter,

the perpendicular distance of the line of action of force from the axis of

rotation is larger as compared to the wheel of short diameter, due to

this the turning effect is large as a result, it becomes easy to turn the

wheel.

13. A spanner (or wrench) has a long handle. Why?

Ans.

A spanner has a long handle because this increases the perpendicular

distance from the axis of rotation which helps in displacing and

replacing the spare parts easily.

14. A jack screw is provided with a long arm. Explain why?

Ans.

A jack screw is provided with a long handle because this increases the

perpendicular distance from the axis of rotation thus making it easier

to lift a load with less amount of force.

16. The adjacent diagram shows a heavy roller, with its axle at O,

which is to be raised on a pavement XY. If there is friction between

the roller and the pavement, show by an arrow on the diagram the

point of application and the direction of force to be applied.

Ans.

18. Draw a neat labeled diagram to show the direction of two

forces acting on a body to produce rotation in it. Also mark the

point O about which the rotation takes place.

Ans.

19. What do you understand by the term couple? State its effect.

Give two examples in our daily life where couple is applied to turn a

body?

Ans.

Two equal and opposite parallel forces not acting along the same line

form a couple.

A couple always produces a rotation.

While turning a water tap.

While turning a steering wheel.

20. Define moment of couple. Write its S.I. unit.

Ans.

The moment of couple is the product of either forces and the

perpendicular distance between the two forces ( or the couple arm).

Its S.I. unit is Newton Meter (Nm)

21. Prove that

Moment of couple = force * couple arm.

Ans.

Moment of force F at the end A

= F * OA

Moment of force F at the end B

= F * OB

Total moment of couple = F * OA + F * OB

= F * (OA + OB)

= F * AB

= F * Couple arm

[Hence Proved]

22. What do you mean by equilibrium of a body?

Ans.

When a number of forces acting on a body produce no change in its

change in its state of rest or linear or rotational motion, the body is

said to be in equilibrium.

23. State the conditions when the body is in [a] Static

equilibrium [b] dynamic equilibrium. Give one example of each of

the static and dynamic equilibrium.

Ans.

When the body remains in rest under the influence of several forces, the

body is in static equilibrium.

E.g.

A body laying on the table top is pulled by a force to its left and an

equal force towards the right.

When a body remains in the same state of motion under the influence of

several forces, the body is said to be in dynamic equilibrium.

E.g.

A rain drop reaching the earth’s surface with a constant velocity.

24. State two conditions for a body, acted upon by several forces

to be in equilibrium.

Ans.

[i] The resultant of all forces acting on a body must be zero.

[ii] The algebraic sum of moments of all forces acting on a body about

a point of rotation should be zero.

25. State the principal of moments. Name one device based on it.

Ans.

According to the principal of moments, if the algebraic sum of moments

of all the forces acting on a body about the axis of rotation is zero, the

body is in equilibrium.

26. Describe a simple experiment to verify the principal of

moments, if you are supplied with a meter scale, a fulcrum and two

springs with slotted weights.

Ans.

Suspend a meter rule horizontally from a fixed support by means of a

strong tread at O as shown in the figure given below.

Now suspend two spring balances A and B on the meter rule on either

side of the thread. Suspend some slotted weights W1 and W2 on the

spring balance. The meter rule may tilt to one side. Now, adjust either

the slotted weights on the spring balance or the position of the spring

balance on either side of thread in such a way that the meter rule again

becomes horizontal.

Let the spring suspended from the spring balance Aon the right side of

the thread be W1 at a distance OA = l1, while the weight suspended from

spring balance B on the left side of the thread be W2 at a distance OB =

l2 .

The weight W1 tends to turn the meter rule clockwise, while the weight

W2 tends to turn the meter rule anticlockwise.

Clockwise moment of weight W1 about the point O = W1 * l1

Anticlockwise moment of weight W2 about the point O = W2 * l2

In equilibrium, when the meter rule is horizontal, it is found that W1l1 =

W2l2

i.e., clockwise moment of force = anticlockwise moment of force.

This verifies the principal of moments.

Lesson-1(B) Centre of Gravity

Q1. Define the term 'centre of gravity' of a body.

A1. The centre of gravity (C.G.) of a body is the point about which the algebraic sum of

moments of weights of all the particles constituting the body is zero.

Q2. Can centre of gravity of a body be situated outside its material? Give an example.

A2. Yes. Example- C.G. of a ring is at its geometric centre where there is no material.

Q3. State the factor on which the position of centre of gravity of a body depends. Explain

your answer with an example.

A3. The position of the centre of gravity of a body of given mass depends on its shape i.e., on

the distribution of mass (of particles) in it.

Example: The centre of gravity of a uniform wire is at the middle of its length. But if the same

wire is bent into the form of a circle, its centre of gravity will then be at the centre of the circle.

Q4. What is the position of centre of gravity of

(a)rectangular lamina(b)cylinder ?

A4. (a) At the point of intersection of its diagonals.

(b)At the midpoint of the axis of cylinder.

Q5. At what point is the centre of gravity situated in:

(a) A rectangular lamina (b) A circular lamina?

A5. (a) At the point of intersection of its medians.

(b) At the centre of circular lamina.

Q6. Where is the centre of gravity of a uniform ring situated?

A6.At the centre of ring.

Q7. Square cardboard is suspended by passing a pin through a narrow hole at its one

corner.Draw a diagram to show its rest position.In the diagram, mark the point of

suspension by the letter S and centre of gravity by the letter G.

A7. For diagrams refer to book.

Q8. Explain how you will determine experimentally the position of centre of gravity of a

triangular lamina or (a triangular piece of cardboard).

A8. Refer to book page 14 fig. 1.40 for diagram (instead of irregular lamina we have to draw a

triangular lamina)

Take a triangular lamina make three holes at a, b, c near the edge of triangular lamina. Now

suspend the given lamina long with a plumb line from hole ‘a’ check that the lamina is free

tooscillateabout the point of suspension. When lamina has come to rest, draw straight line ad

along the plumb line. Repeat the experiment by suspending the lamina through hole 'b' and then

through hole ‘c' for which we get straight lines ad, be andcfrespectively. It is noticed that the

lines ad be and cf intersect each other at a common point G which is the position of centre of

gravity of triangular lamina i.e. the point of intersection of medians.

Q9. Sate whether the following statements are true or false.

(i) The position of centre of gravity of a body remains unchanged even when

the body is deformed. – False

(ii) The centre of gravity of a freely suspended body always lies vertically

below the point of suspension. – True

Q10. A uniform flat circular rim is balanced on a sharp vertical nail by supporting it at a

point A, as shown in fig. 1.41. Mark the position of centre of gravity of the rim in the

diagram by the letter G.

A10. Refer to book and notes (The centre of gravity of a freely suspended body always lies

vertically below the point of suspension).

Q11. Fig. 1.42 shows three pieces of cardboard of uniform thickness cut into three

different shapes. On each diagram draw two lines to indicate the position of centre of

gravity G.

A11. Refer to book page no.13 fig. 1.37.

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Lesson-1(C) Uniform Circular Motion

Q1. Explain the meaning of uniform circular motion. Why is such motion said to be

accelerated?

A1. When a particle moves with a constant speed a circular path, its motion is said to be the

uniform circular motion.

Q2. Draw a neat labelled diagram for a particle moving in a circular path with a constant

speed. In your diagram show the direction of velocity in any instant.

A2. Refer to book page no. 15 fig. 1.43 for diagram.

Q3. Is it possible to have an accelerated motion with a constant speed? Name such type

of motion.

A3. Yes, uniform circular motion.

Q4. Give an example of motion in which speedremains uniform, but the velocity changes.

A4. Circular motion.

Q5. Uniform circular motion is an accelerated motion. Explain it. State whether the

acceleration is uniform or variable? Name the force responsible to cause this

acceleration. What is the direction of force at any instance? Draw a diagram in support of

your answer.

A5. In uniform circular motion, the particle travels equal distance along the circular path in equal

intervals of time, so the speed of particle is uniform, but the direction of motion of the particle

changes at each point of circular path. The continuous change in the direction of motion implies

that the velocity of the particle is non uniform (orvariable motion)i.e., the motion is

accelerated.The acceleration is uniform. The force responsible to cause this acceleration is

centripetal force. The direction of force at any instant is towards the centre of circular path.

For diagram refer to book page no. 16 fig. 1.44.

Q6. Differentiate between a uniform linear motion and a uniform circular motion.

Uniform linear motion Uniform circular motion

Velocity is constant. Velocity is variable.

Acceleration is zero. Acceleration is not equal to zero.

Work done is not zero. Work done is zero.

Displacement is linear. Displacement is angular.

Q7. Name the force required for circular motion. State its direction.

A7. Centripetal force. Its direction is towards the centre of circular path.

Q8. What is centripetal force?

A8. Centripetal force is the force acting on a body moving in a circular path, along the radius

towards the centre.

Q9. Explain the motion of a planet around the sun in a circular path.

A9. A planet revolves around the sun in a circular path such that the necessary centripetal force

is produced by the gravitational force of attraction between the sun and the planets. The planets

moves with a constant speed and variable velocity.

Q10. (a) How does a centripetal force differ from a centrifugal force with reference to the

direction in which they act?

A10(a). In a centripetal force the direction of force is towards the centre of circular path while in

centrifugal force the direction of force is away from the centre of the circular path. They act in

opposite directions.

(b)Is centrifugal force the force of reaction of the centrifugal force?

A10(b). No

(c) Compare the magnitudes of centripetal and centrifugal force.

A10(c) 1:1.

Q11. Is centrifugal force a real force?

A11. No.

Q12. A small pebble tied at one end of a string is placed near the periphery of a circular

disc, at the centre of which the other end of the string is tied to a peg. The disc is rotating

about an axis passing through its centre.

(a) What will be your observation when you are standing outside the disc?

Explain.

(b) What will be your observation when you are standing at the centre of

the disc? Explain.

A12(a). When we stand outside the disc we observe that the pebble moves in a circular path

because the tension in the string provides the centripetal force needed for the circular motion.

A12(b). When we stand at the centre of the disc we observe that the pebbleis stationary just in

front because the centrifugal force on the pebblebalances the tension in the string.

Q13. A piece of stone tied at the end of a thread is whirled in a horizontal circle with

uniform speed with the help of hand. Answer the following questions:

(a) Is the velocity of stone uniform or variable?

(b) Is the acceleration of stone uniform or variable?

(c) What is the direction of acceleration of stone at any instant?

(d) What force does provide the centripetal force required for circular

motion?

(e) Name the force and its direction which acts on the hand.

A13(a). Variable.

A13(b). Variable.

A13(c). Towards the centre of the circular path.

A13(d).Tension in the string.

A13e). The reaction of tension away from the centre of the circular path.

Q14. State two differences between the centripetal and centrifugal force.

Centripetal force Centrifugal force

It is the force acting on a body moving in a circular path along the radius towards the circle.

Force assumed to be acting on a body moving in a circular path in a direction away from the centre of the circular path is called centrifugal force.

It is a real force. It is a non real force.

Its direction is towards the centre. Its direction is away from the centre.

A15. State whether the following statements are true or false.

(a) The earth moves around the sun with uniform velocity. – False

(b) The motion of moon around the earth in circular path is an accelerated motion. –

True

(c) A uniform linear motion is an accelerated, while a uniform circular motion is an

accelerated motion. – True

(d) In a uniform circular motion, the speed continuously changes because the

direction of motion changes. –False

(e) A boy experiences a centrifugal force on his hand when herotates a piece of stone

tied at one end of a string, holding the other end in the hand. – False

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FORCE

1) State the condition when on applying a force, the body has: (a) the translational motion (b) the rotational motion

Ans:- (a)Translational motion takes place when the body is free to move. (b) Rotational motion takes place when the body is pivoted at a point.

2) Define moment of force and state its S.I. unit. Ans:- The turning effect of force produced in a body about a fixed point or axis is known as moment of force or torque. It is equal to the product of the magnitude of the force and the perpendicular distance of the line of action of force from the axis of rotation.

𝜏 = 𝐹 × 𝑑 where F = magnitude of Force and

d= perpendicular distance between line of action of force and axis of rotation The S.I. unit of moment of force is Nm. 3) State the two factors affecting the turning effect of a force.

Ans:- The two factors affecting the turning effect of force are: (1) The magnitude of force applied (2) The perpendicular distance of the line of action of force from the axis of

rotation. 4) What do you mean by positive and negative moment of force? Ans:- If force acting on a pivoted body makes it turn anticlockwise then a positive moment of force is said to be produced. Similarly if force acting on a pivoted body makes it turn clockwise then a negative moment of force is said to be produced. 5) Why is it easier to open a door by applying the force at the free end of it? Ans:- The free end of the door is at the maximum perpendicular distance from the hinge or the point of pivot. So the moment of force required to turn the door can be produced by applying force of least magnitude at the free end. Therefore the door can be opened easily. 6) A spanner (or wrench) has a long handle. Explain why. Ans:- A spanner or wrench is used to tighten or loosen a nut by turning it. As it has a long handle, the perpendicular distance between the line of action of force and the axis of rotation of the nut is more. Therefore a force of less magnitude is sufficient to produce the moment of force required to turn a nut bolt using this spanner or wrench. Hence the nut can be tightened or loosened easily. 7) A jackscrew is provided with a long arm. Explain why. Ans:- A jackscrew is used to lift a heavy load such as a vehicle by applying a very less force. As it has a long arm so the perpendicular distance between the line of action of force and the axis of its rotation is long. This helps to apply a less effort to produce the necessary moment of force. 8) What do you understand by the term couple? State its effect. Give some

examples in our daily life where couple is applied. Ans:- A couple is a pair of equal, opposite and parallel forces not acting along the same line. Its effect is to produce rotation. The examples of couple action in our daily life are:

Turning a water tap, tightening the screw cap of a bottle, turning a key in a lock etc. 9) Define moment of couple. Write its S.I. unit. Ans:- The moment of couple is defined as the product of magnitude of either force and the perpendicular distance between the lines of action of the two forces (couple arm). Its S.I. unit is Nm. 10) What do you mean by equilibrium of a body? Name its two kinds.

Ans:- When a number of forces acting on a body produce no change in its state of rest or of motion then the body is said to be in equilibrium. It is of two kinds namely static equilibrium and dynamic equilibrium. 11) What do you mean by static equilibrium and dynamic equilibrium? Ans:- When a body remains in the state of rest under the influence of several forces, the body is said to be in static equilibrium. Similarly when a body remains in the same state of motion under the influence of the several forces, the body is said to be in dynamic equilibrium. 12) State the two conditions for a body acted upon by several forces to be in

equilibrium. Ans:- Following are the two conditions for a body to remain in equilibrium.

(1) The algebraic sum of all the forces acting on the body should be zero. (2) The algebraic sum of moments of all the forces acting on the body about

the point of rotation should be zero. 13) A book is lying at rest on the surface of horizontal table top. State the kind

of equilibrium possessed by the book. Name and state the direction of different forces acting on the book.

Ans:- The book is at static equilibrium. The forces acting on the book are:

(1) The weight of the book or force of gravity acting in vertically downward direction.

(2) The force of normal reaction of the table surface acting in vertically upward direction.

14) State the kind of equilibrium possessed by a rain drop falling through the atmosphere. Name and state the direction of different forces acting on the rain drop.

Ans:- A rain drop falling through the atmosphere possesses dynamic equilibrium. The different forces acting on the rain drop are as follows:

1) Weight of the raindrop or force of gravity on the raindrop in downward direction.

2) Buoyant force of air in upward direction. 3) Viscous force of air in upward direction.

15) State the principle of moments. Name one device based on it.

Ans:- The principle of moments states that at equilibrium the sum total of

anticlockwise moments is equal to the sum total of clockwise moments of

forces produced in a body about a point of rotation.

A beam balance works on the principle of moments.

16) Define the term centre of gravity of a body.

Ans:- The centre of gravity of a body is the point about which the algebraic

sum of moments of weights of all the particles constituting the body is zero.

The entire weight of the body can be considered to act at this point,

howsoever the body is placed.

17) Can centre of gravity of a body be situated outside its material? Give an

example.

Ans:- Yes, the centre of gravity of a body can be situated outside its material.

e.g. ring, hollow cylinder etc

18) Can centre of gravity of a body be situated outside it? Give an example.

Ans:- Yes, the centre of gravity of a body can be situated outside it.

e.g. L-shaped body, boomerang

19) State the position of centre of gravity of the following with the aid of

diagram.

(a)Rectangular lamina, (b) triangular lamina, (c) circular lamina/circular disc,

(d)ring

Ans:-

a) Rectangular lamina Point of intersection of diagonals

b) Triangular lamina Point of intersection of medians

c) Circular lamina Geometric centre of the circle

d) Ring Geometric centre of the ring

20) State the position of centre of gravity of the following.

(a)straight rod, (b)cylinder, (c)sphere,(d)solid cone, (e) hollow cone

Ans:-

a) Straight rod Mid-point of the rod

b) cylinder Mid-point of axis of the cylinder

c) sphere Geometric centre of the sphere

d) solid cone At a height h/4 from the base, on its axis

where h is vertical height of the cone

e) hollow cone At a height h/3 from the base, on its axis

where h is vertical height of the cone

21) State a factor on which the position of centre of gravity of a body depends.

Explain your answer with an example.

Ans:- The position of centre of gravity of a body of given mass depends on its

shape i.e. on the distribution of mass.

For example the centre of gravity of a uniform wire is at the middle of its

length but if the same wire is bent into the form of a circle then its centre of

gravity will then be at the centre of the circle.

22) State the position of the point with respect to centre of gravity of a body at

which the body can be balanced freely.

Ans:- If a body balances freely about any point then this point of balancing lies

on the same vertical line passing through the centre of gravity of the body.

23) Differentiate between uniform circular motion and uniform linear motion.

Ans:-

Uniform circular motion Uniform linear motion

(i) When a body moves at a constant Speed in a circular path then the motion is called a uniform circular motion.

(ii) Instantaneous direction of motion changes.

(iii) It is an accelerated motion.

(i) When a body moves at a constant Speed in a straight path then the motion is called a uniform linear motion.

(ii) Direction of motion does not change with time.

(iii) It is not an accelerated motion.

24) With the aid of a diagram state the direction of velocity of a

body at any instant in circular path.

Ans:- The instantaneous direction of velocity of a body in the

state of circular motion is tangential to the circular path.

25) Give an example of motion in which speed remains constant but velocity

changes./ Give an example of an accelerated motion with a constant speed.

Ans:- uniform circular motion

26) Explain how a uniform circular motion is an accelerated motion.

Ans:- The direction of motion of a body in the state of uniform circular motion

changes at every instant of time. Therefore the velocity of the body changes

although its speed remains constant. So due to variable velocity of the body,

uniform circular motion is an accelerated motion.

27) State whether the acceleration produced in a uniform circular motion is

uniform or variable. Name the force responsible to cause this

acceleration. With the aid of a diagram state the direction of

this force at any instant?

Ans:- The acceleration of a body in the state of uniform

circular motion is a variable.

The force responsible to cause this acceleration is

centripetal force. It always acts towards the centre of the

circular path.

28) What is a centripetal force?

Ans:- A centripetal force is the one which always acts on a body towards the

centre of the circular path when the body is in the state of uniform circular

motion.

29) Give examples of centripetal force in the following cases:

a) Motion of a stone tied to a string at one end and whirled in a circular path

by holding the other end of the string- The force of tension along the string

acts as the centripetal force.

b) Motion of a planet around the sun- The gravitational force of attraction of

the sun acting on the planet acts as the centripetal force.

c) Motion of a satellite around the earth- The weight of the satellite/ force of

gravity acting on the satellite acts as the centripetal force.

d) Motion of an electron in the orbit around the nucleus- The electrostatic

force of attraction of the nucleus acting on the electron acts as the

centripetal force.

30) Draw a diagram to show (i) the direction of

centripetal force, (ii) the direction of centrifugal

force, (iii) the instantaneous direction of

motion/velocity of a body in the state of uniform

circular motion.

Ans:

31) Write one similarity and one difference between centripetal force and centrifugal force.

Ans:- Similarity:- Both the centripetal force and centrifugal force have equal magnitude. Difference:- Centripetal force acts towards the centre of circular path but centrifugal force acts away from the centre of circular path. 32) Is centrifugal force the force of reaction of the centripetal force? Ans:- No, centrifugal force is not the reaction force of centripetal force. 33) Between centripetal and centrifugal force, which is not a real force? Ans:- Centrifugal force is not a real force.

Chapter 2

Work, Energy and Power

EXERCISE 2(A)

1. Define work. When is work said to be done by

a force?

Ans. Work done by the force is defined as the

product of magnitude of force and the

displacement of point of application of force.

Work is said to be done by a force only when

the force applied causes a displacement of the

body.

2. How is the work done by a force measured

when

(i) force is in direction of displacement

(ii) force is at an angle to the direction of

displacement

Ans. (i) W = F*S

Where W = Work done

F= Force applied

S = Displacement caused by force

(iii) W = F S cos 𝜽

W = Work done

F= Force applied

S = Displacement caused by force

𝜽=Angle between force and

displacement

3. Refer to book

4. A body is acted upon by a force. State two

conditions when the work done is zero.

Ans. Two conditions when the work done is zero

are :

(i) When there is no displacement i.e. S = 0

(ii) When the displacement is normal to the

direction of force i.e. 𝜽= 90°

5. State the condition when the work done by a

force is (a)positive, (b) negative. Explain with

the help of examples.

Ans. (a) The work done by a force is said to be

positive when the displacement is in the

direction of force and 𝜽 = 0°.For example, Work

done in the free fall of a body such that W = FS

=mgh where m= mass of body, g= acceleration

due to gravity, h= height of body under gravity.

(b) Work done is said to be negative when the

displacement is opposite to the direction of force

and 𝜽 = 180°.For example, Work done by a

cricketer in catching the ball such that force is

applied in forward direction and displacement

occurs in the backward direction.

6. Refer to book

7. Refer to book

8. Refer to book

9. Refer to book

10. Refer to book

11. Refer to book

12. Refer to book

13. What are the S.I. and C.G.S. units of work?

How are they related? Establish the relationship.

Ans. The S.I. and C.G.S. units of work are joule(J)

and erg respectively.

1 joule = 1 N* 1 m

= 105 dyne * 102 cm

= 107 dyne* cm

= 107 erg

14. State and define the S.I. unit of work.

Ans. The S.I. unit of Work is Joule(J).

1 joule of work is said to be done when a

force of 1 newton displaces a body through a

distance of 1 metre in its own direction.

15. Express joule in terms of erg.

Ans. 1 joule =107 erg

16. A body of mass m falls down through a height

h. Obtain an expression for the work done by the

force of gravity.

Ans. W= FS= mgh

Where W= Work done

F= Force applied

S= Displacement caused by force

m= mass of body

g= acceleration due to gravity

h= height of body under gravity

17. Refer to book

18. Define the term energy and state its S.I. unit.

Ans. Energy is the capacity to do work.

Its S.I. unit is joule (J).

19. Refer to book

20. Refer to book

21. Refer to book

22. Define a kilowatt hour. How is it related to

joule?

Ans. One kilowatt hour is the energy spent by a

source of power 1 watt in 1 hour.

1 kWh= 3.6 * 106 J

23. Define the term power. State its S.I. unit.

Ans. The rate of doing work is called power.

Its S.I. unit is watt (W).

24. State two factors on which power spent by a

source depends. Explain your answer with

examples.

Ans. Two factors on which power spent by a

source depends are :

(i) The amount of work done by the

source(P∝W)

For example, if boy A does 1 joule of work in

a certain time and boy B does 2 joule of work

in the same time, then the power of boy B is

more.

(ii) The time taken by the source to do the said

work(P∝𝟏

𝒕)

For example, if coolie A does a certain work

in 1 minute and coolie B does the same work

in 2 minutes, then power of coolie A is more.

25. Differentiate between work and power.

Ans.

WORK POWER 1. Work done by a source is equal to the product of work done and the displacement in the direction of force.

1. Power of a source is the rate of doing work by it.

2. It does not depend on time.

2. It depends on time in which the work is done.

3. Its S.I. unit is joule. 3. Its S.I. unit is watt.

26. Differentiate between energy and power.

Ans.

ENERGY POWER 1. Energy of a body is

its capacity to do work.

1. Power of a source is the rate at which energy is supplied by it.

2. It does not depend on time.

2. It depends on time in which the energy is spent.

3. Its S.I. unit is joule. 3. Its S.I. unit is watt.

27. State and define the S.I. unit of power.

Ans. The S.I. unit of power is watt (W).

If 1 joule of work is done in 1 second, the

power spent is said to be 1 watt.

28. (a) Name the physical quantity measured in

terms of horse power.

(b) How is horse power related to S.I. unit of

power?

Ans. (a) Energy

(b) 1 H.P. = 746 W

29. Differentiate between watt and watt hour.

Ans.

WATT WATT HOUR 1. If 1 joule of work is

done in 1 second, the power is said to be 1 watt.

1. One watt hour is the energy spent by a source of power 1 watt in 1 hour.

2. It depends on time in which the energy is spent.

2.It does not depend on time.

3. It is a unit of power. 4. It is a unit of energy.

30. Refer to book

31. Refer to book