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 –
- A force should be applied on the object.
- 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 –
- A man is applying a force on a stationary truck.
- 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.
- A man pushing a rigid wall.
Q- 12 What type of energy transformation takes place in the following situations –
- Electric motor
Ans – Chemical energy Electrical energy Light energy + Heat energy
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