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# Chapter 11 Work and Energy Interview Questions Answers

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Question 1 : A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force. Let us take it that the force acts on the object through the displacement. What is the work done in this case?

When a force F acts on an object to move it in its direction through a distance S, the work is done
The work on the body is done by force
Work done = Force × Displacement
W = F × S
Where,
F = 7 N S = 8 m
So, work done,
W = 7 × 8
W = 56 Nm
W = 56 J

Question 2 : When do we say that work is done?

Work is completed whenever the given conditions are satisfied:
(i) A force acts on the body.
(ii) There’s a displacement of the body caused by the applied force on the direction of the applied force.

Question 3 : Write an expression for the work done when a force is acting on an object in the direction of its displacement.

When a force F displaces a body through a distance S within the direction of the applied force, then the work done W on the body is given by the expression:
W = F × S

Question 4 : Define 1 J of work.

Answer 4 : 1 J is that the quantity of labor done by a force of one N on associate degree object that displaces it through a distance of one m within the direction of the applied force.

Question 5 :
A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long.
How much work is done in ploughing the length of the field?

Work done by the bullocks is given by the expression:
W= F × d
Where,
Applied force, F = 140 N
Displacement, d = 15 m
W= a hundred and forty × fifteen = 2100 J
Hence, 2100 J of labour is finished in tilling the length of the sector.

Question 6 : What is the kinetic energy of an object?

Answer 6 : The energy possessed by a body by the virtue of its motion is termed mechanical energy or kinetic energy. Every moving object possesses mechanical energy. A body uses mechanical energy to try to work. Kinetic energy of the hammer is employed in driving a nail into a log of wood, mechanical energy of air is employed to run wind mills, etc.

Question 7 : Write an expression for the kinetic energy of an object.

If a body of mass m is moving with a speed v, then its K.E. E k is given by the expression,
Ek = 1/2 m v2
Its SI unit is Joule (J).

Question 8 : The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?

Answer 8 : Question 9 : What is power?

Answer 9 : Power is that the rate of doing work or the speed of transfer of energy. If W is that the quantity of work wiped out time t, then power is given by the expression, P = W/T
It is expressed in watt (W).

Question 10 : Define 1 watt of power.

A body is claimed to possess power of one watt if it will work on the speed of 1 joule in 1 s.
That is,
One W = 1 J/1 S

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