December 2, 2022

# Work and energy questions Class 9 science Chapter 11

## Work and energy questions Class 9 Science Chapter 11

Work and energy extra questions for term 2 exams very short questions, short questions and numericles topic wise. This chapter is very important for exam preparation.

Class 9 Science

Chapter 11 Work, Power and Energy

Extra Questions – Topicwise

Topic – WORK

Q- 1 What is negative work ?

Ans – When Force and displacement are in opposite directions Then the work will be negative.

So W = Force and displacement

W = F x (-S) (Let displacement is in opposite direction)

W = – FS

Q- 2 What is work ? What are the conditions required for work to be done?

Ans – When a force is applied on an object and gets displaced, in that situation work is done.

W = F x S

So There is two conditions required for work to be done –

1. A force should be applied on the object.
2. Object should get displaced.

Q- 3 Write an example for negative work and positive work.

Ans – Negative work – When we walk, frictional force does the work backward direction and we move forward. Force and displacement is in opposite direction. Then work is negative.

Positive work – When we exert a force on car and car moves in the direction of the car the work is positive.

Q- 4 What is the SI unit of Work.

Ans – Joule (J)

Q- 5 Which type of work is done When force and displacement are perpendicular to each other?

Ans – In that case no work is done. When the force is perpendicular to the displacement.

W = FS Cosϴ

= FS cos 90

W = 0 (Cos 90 = 0)

Q- 6 Write an example of zero work.

Ans – A coolie carries load on the head. In that case force and displacement are perpendicular. Then work is zero.

Q- 7 When a girl is walking around a circular path. How much work is done by the girl?

Ans – Displacement will be zero so work is also zero.

Q- 8 What is the amount of work done by a man in pushing a wall with 500N force.

Ans – Wall has not displaced so no work is done.

W = F x S

= 500 x 0

= 0 joule

Q- 9 Give an example each of potential energy (i) due to position (ii) due to shape.

Ans – Example for potential energy due to position – A ball is at some height from the surface of earth.

Example for potential energy due of shape – A spring possesses potential energy when it gets stretched, when it is released, its potential energy changes into kinetic energy.

Q- 10 How is kilowatt and kilowatt hour?

Ans – Kilowatt is the unit of power and kilowatt hour is the unit of energy.

Q- 11 Give examples of an object, which is not displaced in spite of this, a force acting on it.

Ans – There are some examples –

1. A man is applying a force on a stationary truck.
2. A coolie carrying a load on his head and standing still. Here is no displacement for the load but force is applied by coolie and a gravitational force is also working.
3. A man pushing a rigid wall.

Q- 12 What type of energy transformation takes place in the following situations –

1. Electric motor

Ans – Chemical energy Electrical energy Light energy + Heat energy

2. Dynamo

Ans – Mechanical energy Electrical energy

3. Steam engine

Ans – Heat energy Mechanical energy

4. Electric Heater

Ans – Chemical energy Heat energy

5. Spring of a watch

Ans – Potential energy Kinetic energy

6. Thermal power station

Ans – Heat energy Electric energy

7. Electric cell

Ans – Chemical energy Electrical energy

Q- 13 Can kinetic energy of a body be negative?

Ans – No, because E = ½ mv²

Now, m can’t be negative and v² will be positive.

Q- 14 What will be the angle between force and displacement in the case of zero work?

Ans – at 90º.

Q- 15 What will be the angle between force and displacement in the case of negative work?

Ans – at 180º.

Q- 16 If speed is doubled then what will be the impact of it on kinetic energy?

Ans – Kinetic energy will be 4 times.

Q- 17 What is the relationship between the commercial unit and SI unit of energy?

Ans – 1 unit of energy = 1 KWh = 3.6 x 10⁶ Joule