NCERT Solutions Class 9 Scinece Chapter 11 Work And Energy Download In Pdf

Chapter 11 Work And Energy Download in pdf

NCERT Solutions Intext Questions Page no.149

**Question 1.** When do we say that work is
done?

**Question 2.** Write an expression for the work
done when a force is acting on
an object in the direction of its
displacement.

**Question 3.** Define 1 J of work.

**Question 4. **A pair of bullocks exerts a force
of 140 N on a plough. The field
being ploughed is 15 m long.
How much work is

done in
ploughing the length of the field?

NCERT Solutions Intext Questions Page no.152

**Question 1.** What is the kinetic energy of an
object?

**Question 2.** Write an expression for the kinetic
energy of an object.

**Question 3. **The kinetic energy of an object of
mass, m moving with a velocity
of 5 m s–1 is 25 J. What will be its
kinetic energy when its velocity
is doubled? What will be its
kinetic energy when its velocity
is increased three times?

NCERT Solutions Intext Questions Page no.156

**Question 1. **What is power?

**Question 2.** Define 1 watt of power.

**
Question 3.** A lamp consumes 1000 J of
electrical energy in 10 s. What is
its power?

**Question 4.** Define average power.

NCERT Solutions Exercises Question

**Question 1. **Look at the activities listed below. Reason out whether or not
work is done in the light of your understanding of the term
‘work’.

• Suma is swimming in a pond.

• A donkey is carrying a load on its back.

• A wind-mill is lifting water from a well.

• A green plant is carrying out photosynthesis

• An engine is pulling a train.

• Food grains are getting dried in the sun.

• A sailboat is moving due to wind energy.

**Question 2. **An object thrown at a certain angle to the ground moves in a
curved path and falls back to the ground. The initial and the
final points of the path of the object lie on the same horizontal
line. What is the work done by the force of gravity on the object?

**Question 3.** A battery lights a bulb. Describe the energy changes involved
in the process.

**Question 4.** Certain force acting on a 20 kg mass changes its velocity from
5 m s–1 to 2 m s–1. Calculate the work done by the force.

**
Question 5. **A mass of 10 kg is at a point A on a table. It is moved to a point
B. If the line joining A and B is horizontal, what is the work
done on the object by the gravitational force? Explain your
answer.

**Question 6.** The potential energy of a freely falling object decreases
progressively. Does this violate the law of conservation of
energy? Why?

**Question 7. **What are the various energy transformations that occur when
you are riding a bicycle?

**Question 8. **Does the transfer of energy take place when you push a huge
rock with all your might and fail to move it? Where is the
energy you spend going?

**Question 9.** A certain household has consumed 250 units of energy during
a month. How much energy is this in joules?

**Question 10.** An object of mass 40 kg is raised to a height of 5 m above the
ground. What is its potential energy? If the object is allowed to
fall, find its kinetic energy when it is half-way down.

**Question 11. **What is the work done by the force of gravity on a satellite
moving round the earth? Justify your answer.

**
Question 12.** Can there be displacement of an object in the absence of any
force acting on it? Think. Discuss this question with your friends
and teacher.

**Question 13.** A person holds a bundle of hay over his head for 30 minutes
and gets tired. Has he done some work or not? Justify your
answer.

**Question 14. **An electric heater is rated 1500 W. How much energy does it
use in 10 hours?

**Question 15. **Illustrate the law of conservation of energy by discussing the
energy changes which occur when we draw a pendulum bob to
one side and allow it to oscillate. Why does the bob eventually
come to rest? What happens to its energy eventually? Is it a
violation of the law of conservation of energy?

**Question 16.** An object of mass, m is moving with a constant velocity, v.
How much work should be done on the object in order to bring
the object to rest?

**Question 17.** Calculate the work required to be done to stop a car of 1500 kg
moving at a velocity of 60 km/h?

**Question 18.** In each of the following a force, F is acting on an object of
mass, m. The direction of displacement is from west to east
shown by the longer arrow. Observe the diagrams carefully
and state whether the work done by the force is negative,
positive or zero.

**Question 19.** Soni says that the acceleration in an object could be zero even
when several forces are acting on it. Do you agree with her?
Why?

**Question 20. **Find the energy in kW h consumed in 10 hours by four devices
of power 500 W each.

**Question 21. **A freely falling object eventually stops on reaching the ground.
What happenes to its kinetic energy?

Please send your queries to ncerthelp@gmail.com you can aslo visit our facebook page to get quick help. Link of our facebook page is given in sidebar

- Chapter 3 Atoms and Molecules
- Chapter 1 Matter In Our Surroundings
- Chapter 2 Is Matter Around Us Pure
- Chapter 4 Structure of The Atom
- Chapter 5 The Fundamental Unit of Life
- Chapter 7 Diversity In Living Organisms
- Chapter 8 Motion
- Chapter 9 Force and Laws of Motion
- Chapter 10 Gravitation
- Chapter 11 Work And Energy
- chapter 12 Sound
- Chapter 13 Why Do We Fall Ill
- Chapter 14 Natural Resources
- Chapter 15 Improvement In Food Resources

- NCERT Solutions for Class 9 Science Maths Hindi English Math
- NCERT Solutions for Class 10 Maths Science English Hindi SST
- Class 11 Maths Ncert Solutions Biology Chemistry English Physics
- Class 12 Maths Ncert Solutions Chemistry Biology Physics pdf

- Class 1 Model Test Papers Download in pdf
- Class 5 Model Test Papers Download in pdf
- Class 6 Model Test Papers Download in pdf
- Class 7 Model Test Papers Download in pdf
- Class 8 Model Test Papers Download in pdf
- Class 9 Model Test Papers Download in pdf
- Class 10 Model Test Papers Download in pdf
- Class 11 Model Test Papers Download in pdf
- Class 12 Model Test Papers Download in pdf

Copyright @ ncerthelp.com A free educational website for CBSE, ICSE and UP board.