Question 1

Question 1:
How much work is done when a body of mass m is raised to a height h above the ground?

Accepted Answer

Answer:
We can calculate the work done against gravity in moving a body of mass  (m) by a height (h) as, Work done in lifting a body = (Weight of body) (Vertical distance)
So, W = (m) (g) (h)

Question 2

Question 2:
State the SI unit of work.

Accepted Answer

Answer:
Joule is the SI unit of work. It is denoted by ‘J.

Question 3

Question 3:
Is work a scalar or a vector quantity?

Accepted Answer

Answer:
Work is a scalar quantity as it has only magnitude.

Question 4

Question 4:
Define 1 joule of work.

Accepted Answer

Answer:
Joule is the SI unit of work. Work done is said to be of 1 Joule when a force of 1 Newton moves a body by 1 m along the direction of the force applied.

Question 5

Question 5:
What is the condition for a force to do work on a body?

Accepted Answer

Answer:
The necessary condition for force to do work is that the applied force should produce motion in the body in any direction except the direction perpendicular to the force applied.

Question 6

Question 6:
Is energy a vector quantity?

Accepted Answer

Answer:
No, energy is a scalar quantity as it has only magnitude.

Question 7

Question 7:
What are the units of (a) work, and (b) energy?

Accepted Answer

Answer:
The units of work and energy are the same.
(a) Work - Joule (J)
(b) Energy - Joule (J)

Question 8

Question 8:
What is the work done against gravity when a body is moved horizontally along a frictionless surface?

Accepted Answer

Answer:
When a body is moved horizontally along a frictionless surface, the work done against gravity is zero because the direction of motion of the body is perpendicular to the direction of the gravitational force.

Question 9

Question 9:
By how much will the kinetic energy of a body increase if its speed is doubled?

Accepted Answer

Answer:
Kinetic energy of a body is directly proportional to the square of velocity. So, the kinetic energy will become four times the initial value when velocity is doubled.

Question 10

Question 10:
Write an expression for the kinetic energy of a body of mass m moving with a velocity v.

Accepted Answer

Answer:
The expression for kinetic energy is as follows:
K.E=21​mv2
 Where,
 (K.E) - Kinetic Energy
(m) - Mass
(v) - Velocity

Question 11

Question 11:
If the speed of a body is halved, what will be the change in its kinetic energy?

Accepted Answer

Answer:
Kinetic energy of a body is directly proportional to the square of velocity. So, the kinetic energy will become (41​) the initial kinetic energy when velocity is halved.

Question 12

Question 12:
On what factors does the kinetic energy of a body depend?

Accepted Answer

Answer:
The kinetic energy of a moving body depends upon two factors. It is directly proportional to the following:
(i) The mass of the moving body
(ii) The square of the velocity of the moving body

Question 13

Question 13:
Which would have a greater effect on the kinetic energy of an object : doubling the mass or doubling the velocity?

Accepted Answer

Answer:
Kinetic energy of a body is directly proportional to the mass and square of velocity of the moving body. So, doubling the velocity will have a greater effect on the kinetic energy of a body.

Question 14

Question 15:
State whether the following objects possess kinetic energy, potential energy, or both :

(a) A man climbing a hill
(b) A flying aeroplane
(c) A bird running on the ground
(d) A ceiling fan in the off position
(e) A stretched spring lying on the ground.

Accepted Answer

Answer:
(a) A man climbing up a hill has both kinetic energy as well as potential energy.
(b) A flying aeroplane has both kinetic energy as well as potential energy.
(c) A bird running on the ground possesses only kinetic energy.
(d) When switched off, a ceiling fan possesses only potential energy.
(e) A stretched spring lying on the ground possesses potential energy.

Question 15

Question 18:
Is potential energy a vector or a scalar quantity?

Accepted Answer

Answer:
Potential energy is a scalar quantity as it has only magnitude.

Chapter 4 : Work and Energy