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CBSE Class 9 Science Worksheet

Unit 3-Motion, Force and Work - Work and energy

1.
An engine produces a power of 10kW. How much time will it raise a mass of 100 kg through a height of 40m ?
2.
What is the time taken by 50W bulb to consume 1500J of energy?
3.
Ramesh can run with a speed of 5 m/s against the frictional force of 20 N, and Suresh can move with a speed of 4 m/s against the frictional force of 30 N. Who is more powerful and why?
4.
An electric heater is rated 1000 W. How much energy does it use in 2 hours?
5.
Choose the correct option: A ball is falling from height h from the ground on the top of building. After it has fallen at a height h/2, it will possess __________.
A) Only potential energy B) Only kinetic energy C) half kinetic and half potential energy D) None of these
6.
Choose the correct option: If the velocity of a car is increased is by 2 times then its kinetic energy ________.
A) increases by 4 times B) increases by 2 times C) decreases by 4 times D) decreases by 4 times
7.
A person carries a body of 10 kg from the ground and put it 2 m above the ground. Calculate the work done by him on the body.
8.
A boy of mass 50 kg runs up a staircase of 30 steps in 9 s. If the height of each step is 12 cm, find his power.
9.
Find the mass an object of mass moving with a velocity of 6 m/s whose kinetic energy is 72J
10.
A light and a heavy object have the same momentum. Which one has a larger kinetic energy?
11.
Fill in the blanks: The __________ is the main source of energy on planet Earth.
12.

 Energy can 

A)

be created but can not be destroyed

B)

not be created but can be destroyed

C)

neither be created nor be destroyed

D)

be created can be destroyed

13.
A person of mass 60 kg reaches the top of the building of height 20 m in 10 seconds. Find his power.
14.
Choose the correct option: Total energy of body when it falls from the top of the roof towards the Earth _________.
A) increases B) decreases C) remains constant D) None of these
15.
An object of mass 15 kg is at a certain height above the ground. If the potential energy of the object is 450 J, find the height at which the object is with respect to the ground.
16.
Fill in the blanks: Car A has a mass of 500 kg and a speed of 50 km/h, and car B has a mass of 1000 kg and a speed of 25 km/h.  The kinetic energy of car A is ___________ of car B
17.
Fill in the blanks: The work done on the object of mass m moving with a velocity v, in order to bring it to the rest is _______.
18.
Fill in the blanks: On a rough surface pulling is _______________ than pushing.
19.
Choose the correct option: If force acts perpendicular to the direction of the displacement, then the work done by the force is _________.
A) zero B) positive C) negative D) either positive or negative
20.
Fill in the blanks: The work done by force of gravity on a satellite moving around the Earth is __________.

CBSE Class 9 Science Worksheet

Unit 3-Motion, Force and Work - Work and energy

Answers

1.
4seconds
2.
30s
3.
Power of Ramesh = 5 X 20 = 100W, Power of Suresh = 4 X 30 = 120W. Hence, Suresh is more powerful.
4.
7200kJ
5.
Option B
6.
Option A

7.
200J
8.
200W
9.
4kg
10.
Lighter object
11.
Sun
12.
Option C

Solution:

Law of Conservation of Energy states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another. For example, turning on a light would seem to produce energy; however, it is electrical energy that is converted to light.


13.
1200W
14.
Option C

15.
3m
16.
twice
17.
0.5mv2
18.
easier
19.
Option A

20.
zero

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