# Balbharati solutions for Science and Technology 9th Standard Maharashtra State Board chapter 2 - Work and Energy [Latest edition]

## Chapter 2: Work and Energy

Exercise
Exercise [Pages 28 - 29]

### Balbharati solutions for Science and Technology 9th Standard Maharashtra State Board Chapter 2 Work and Energy Exercise [Pages 28 - 29]

Exercise | Q 1.1 | Page 28

Explain the difference between potential energy and kinetic energy.

Exercise | Q 1.2 | Page 28

Derive the formula for the kinetic energy of an object of mass m, moving with velocity v.

Exercise | Q 1.3 | Page 28

Prove that the kinetic energy of a freely falling object on reaching the ground is nothing but the transformation of its initial potential energy.

Exercise | Q 1.4 | Page 28

Determine the amount of work done when an object is displaced at an angle of 30^circ with respect to the direction of the applied force.

Exercise | Q 1.5 | Page 28

If an object has 0 momentum, does it have kinetic energy? Explain your answer.

Exercise | Q 1.6 | Page 28

Why is the work done on an object moving with uniform circular motion zero?

Exercise | Q 2.1 | Page 28

Choose one or more correct alternatives.
For work to be performed, energy must be ________

(i) transferred from one place to another
(ii) concentrated
(iii) transformed from one type to another
(iv) destroyed

Exercise | Q 2.2 | Page 28

Choose one or more correct alternatives.
Joule is the unit of ________
(i) force
(ii) work
(iii) power
(iv) energy

Exercise | Q 2.3 | Page 28

Choose one or more correct alternatives.
Which of the forces involved  in dragging a heavy object on a smooth, horizontal surface, have the same magnitude?
(i) the horizontal applied force
(ii) gravitational force
(iii) reaction force in vertical direction
(iv) force of friction

Exercise | Q 2.4 | Page 28

Choose one or more correct alternatives.
Power is a measure of the _______
(i) the rapidity with which work is done
(ii) amount of energy required to perform the work
(iii) The slowness with which work is performed
(iv) length of time

Exercise | Q 2.5 | Page 29

Choose one or more correct alternatives.
While dragging or lifting an object, negative work is done by ________
(i) the applied force
(ii) gravitational force
(iii) frictional force
(iv) reaction force

Exercise | Q 3.1 | Page 28

Rewrite the following sentence using proper alternative.
The potential energy of your body is least when you are _____________

• sitting on a chair

• Sitting on the ground

• sleeping on the ground

• standing on the ground

Exercise | Q 3.2 | Page 28

Rewrite the following sentence using proper alternative.
The total energy of an object falling freely towards the ground ___________

• decreases

•  remains unchanged

• increases

• increases in the beginning and then decreases

Exercise | Q 3.3 | Page 28

Rewrite the following sentence using proper alternative.
If we increase the velocity of a car moving on a flat surface to four times its original speed, its potential energy ____________

• will be twice its original energy

• will not change

• will be 4 times its original energy

• will be 16 times its original energy.

Exercise | Q 3.4 | Page 28

Rewrite the following sentence using proper alternative.
The work done on an object does not depend on _______

• displacement

• applied force

• initial velocity of the object

• the angle between force and displacement.

Exercise | Q 4 | Page 29
Study the following activity and answer the questions.

1. Take two aluminium channels of different lengths.
2.  Place the lower ends of the channels on the floor and hold their upper ends at the same height.
3.  Now take two balls of the same size and weight and release them from the top end of the channels. They will roll down and cover the same distance.

Questions

1. At the moment of releasing the balls, which energy do the balls have?
2. As the balls roll down which energy is converted into which other form of energy?
3. Why do the balls cover the same distance on rolling down?
4. What is the form of the eventual total energy of the balls?
5. Which law related to energy does the above activity demonstrate? Explain.
Exercise | Q 5.1 | Page 29

Solve the following example.
An electric pump has 2 kW power. How much water will the pump lift every minute to a height of 10 m?

Exercise | Q 5.2 | Page 29

Solve the following example.
If a 1200 W electric iron is used daily for 30 minutes, how much total electricity is consumed in the month of April?

Exercise | Q 5.3 | Page 29

Solve the following example.
If the energy of a ball falling from a height of 10 metres is reduced by 40%, how high will it rebound?

Exercise | Q 5.4 | Page 29

Solve the following example.
The velocity of a car increase from 54 km/hr to 72 km/hr. How much is the work done if the mass of the car is 1500 kg?

Exercise | Q 5.5 | Page 29

Solve the following example.
Ravi applied a force of  10 N and moved a book 30 cm in the direction of the force. How much was the work done by Ravi?

Exercise

## Balbharati solutions for Science and Technology 9th Standard Maharashtra State Board chapter 2 - Work and Energy

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Concepts covered in Science and Technology 9th Standard Maharashtra State Board chapter 2 Work and Energy are Transformation of Energy, Law of Conservation of Energy, Free Fall, Concept of Power, Definition of Work, Types of Mechanical Energy: Kinetic Energy, Types of Mechanical Energy: Potential Energy, Concept of Energy, Introduction of Work, Measurement of Work, Mechanical Energy and Its Different Forms.

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