# CBSE Class 9 Science Work and Energy assignment

Read and download free pdf of CBSE Class 9 Science Work and Energy assignment. Get printable school Assignments for Class 9 Science. Class 9 students should practise questions and answers given here for Chapter 11 Work And Energy Science in Class 9 which will help them to strengthen their understanding of all important topics. Students should also download free pdf of Printable Worksheets for Class 9 Science prepared as per the latest books and syllabus issued by NCERT, CBSE, KVS and do problems daily to score better marks in tests and examinations

## Assignment for Class 9 Science Chapter 11 Work And Energy

Class 9 Science students should refer to the following printable assignment in Pdf for Chapter 11 Work And Energy in Class 9. This test paper with questions and answers for Class 9 Science will be very useful for exams and help you to score good marks

### Chapter 11 Work And Energy Class 9 Science Assignment

Question : A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force. Let us take it that the force acts on the object through the displacement. What is the work done in this case?
Answer :  When a force F acts on an object to displace it through a distance S in its direction, then the work done W on the body by the force is given by:
Work done = Force × Displacement
W = F × S
Where,
F = 7 N
S = 8 m
Therefore, work done, W = 7 × 8
= 56 Nm
= 56 J

Question : When do we say that work is done?
Answer :  Work is done whenever the given conditions are satisfied:
(i) A force acts on the body.
(ii) There is a displacement of the body caused by the applied force along the direction of the
applied force.

Question : Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Answer :  When a force F displaces a body through a distance S in the direction of the applied force, then the
work done W on the body is given by the expression:
Work done = Force × Displacement
W = F × s

Question : Define 1 J of work.
Answer :  1 J is the amount of work done by a force of 1 N on an object that displaces it through a distance of 1 m in the direction of the applied force. 80

Question : 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?
Answer :  Work done by the bullocks is given by the expression:
Work done = Force × Displacement
W = F × d
Where,
Applied force, F = 140 N
Displacement, d = 15 m
W = 140 × 15 = 2100 J
Hence, 2100 J of work is done in ploughing the length of the field.

Question : What is the kinetic energy of an object?
Answer :  Kinetic energy is the energy possessed by a body by the virtue of its motion. Every moving object possesses kinetic energy. A body uses kinetic energy to do work. Kinetic energy of hammer is used in driving a nail into a log of wood, kinetic energy of air is used to run wind mills, etc.

Question : Write an expression for the kinetic energy of an object.
Answer :  If a body mass m is moving with a velocity v, then its kinetic energy Ek is given by the expression,
Ek= ½ mv2.
Its SI unit is Joule (J).

Question : 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?
Answer :  Expression for kinetic energy
Ek= ½ mv2
m = Mass of object
v = Velocity of the object in ms−1
Given that kinetic energy, Ek=25J
(i) If the velocity of an object is doubled, then v = 5 × 2 = 10 ms−1.
Therefore, its kinetic energy becomes 4 times its original value, because it is proportional to the square of the velocity.
Hence, kinetic energy = 25 × 4 = 100 J.
(ii) If velocity is increased three times, then its kinetic energy becomes 9 times its original value, because it is proportional to the square of the velocity. Hence, kinetic energy = 25 × 9 = 225 J.80

Question :  What is power?
Answer :  Power is the rate of doing work or the rate of transfer of energy. If W is the amount of work done
in time t, then power is given by the expression,
Power = Work/Time = Energy/Time
P=W/T
It is expressed in watt (W).

Question : Define 1 watt of power:
Answer :  A body is said to have power of 1 watt if it does work at the rate of 1 joule in 1 s,
i.e.,
1W=1J/1s

Question : A lamp consumes 1000 J of electrical energy in 10 s. What is its power?
Answer :  Power is given by the expression,
Power=Work done /Time
Work done = Energy consumed by the lamp = 1000 J
Power=1000 / 10 = 100 Js−1
= 100 W

Question :  Define average power.
Answer :  A body can do different amount of work in different time intervals. Hence, it is better to find average power. Average power is obtained by dividing the total amount of work done in the total time taken to do this work.
Average Power =Total work done / Total time taken

Question : What is energy of a body?

Question : Define kinetic energy.

Question : What is potential energy?

Question : What will be the work done by a force if displacement of the body is zero?

Question : When is work done on a body positive?

Question : Can energy be converted from one form to another?

Question : Define power.

Question : What will be the new kinetic energy of a body if its velocity is doubled?

Question : What will be the potential energy of an object of mass 5 kg kept at a height of 10 metres from the ground? Take g = 10 m/s2.

Question : A green plant is carrying out photosynthesis. What is the work done in this process?

Question : What is mechanical energy of an object?

Question : How we can define one watt?

Question : Give a mathematical expression for the work done when a force is acting on an object in the direction of its displacement.

Question : How average power can be calculated?

Question : When a ball is thrown in upward direction, work is done by the force of gravity. When a ball comes down freely towards the earth, in this case too work is done by the force of gravity. What is the difference in the nature of work done in the two cases?

Question : When work done is positive on a body?

Question : What will be the new kinetic energy of a body if its velocity is doubled?

Question : A constant force of 10N displaces a body through 5 m. Find the work done by the force?

Question : What will be the work done if a stone of mass 2 kg is raised through a height of 10cm?

Question : An object of mass 10kg is moving with speed 4 m/sec. What is the kinetic energy of the object?

Question : An object of mass 10kg is at a certain height above the ground. If the potential energy of the object is 200J. Find the height of the object from the ground.

Question : A person is holding a heavy bag on his head for 20 minutes and gets tired. Has he done some work or not? Explain.

Question : A body of mass5 kg is kept on a table. If it is displaced by a force of 10N by 2 m on the table on the same horizontal line, find the work done by the gravitational force.

Question : What is law of conservation of energy?

Question : A man of mass 50kg climbs a tower of height 45m in 5 seconds with the help of a rope. Find the power of the man.

Question : If a particle falls through a height; its potential energy decreases. Does this violate the law of conservation of energy? Explain why?

Question : A ball of mass 2kg is kept on a tower of height 30m. Find its potential energy at this point. If it is allowed to fall freely, find its kinetic energy when it just touches the ground.

Question : What is the work done by the force of gravity on a satellite moving round the earth?

Question : What will be the work done to stop a moving cycle of mass 30kg which is moving with speed 54km/hr ?

Question : A freely falling body stops when it hits the ground. What happens to its kinetic energy?

Question : Prove that the kinetic energy of a body moving with speed v is equal to 1/2 mv2.

Exam Questions NCERT Class 9 Science Chapter 11 work And Energy

Question. Name the transformation of energy involved in the following cases :
(a) When a body is thrown upwards.
(b) When a body falls from the top of a hill.
(c) When coal burns.
(d) When a gas burns.
(e) When water falls from a height.
Ans : (a) Kinetic energy into potential energy.
(b) Potential energy into kinetic energy.
(c) Chemical energy into heat energy.
(d) Chemical energy into heat energy.
(e) Potential energy into kinetic energy.

Question. What are the factors on which the work done depends?

Ans : The work done by a force depends upon :
(i) The magnitude of the force.
(ii) The magnitude of the displacement.
(iii) The angle between force and displacement.

Question. What is power? What is its SI unit?
Ans :
It is defined as the rate of doing work. Its unit is watt.

Question. Which type of energy is present in a battery?
Ans : Chemical energy.

Question. Name the energy present in an object due to its position or configuration.

Ans : Potential energy.

Question. Give one example of potential energy due to position.

Ans : Water stored in the reservoir of a dam has potential energy.

Question. (a) An arrow moves forward when released from a stretched bow. Explain the transformation of energy in the process.
(b) A boy of mass 50 kg climbs up a vertical height of 100 m. Calculate the amount of potential energy he gains.
Ans : (a) When the bow is stretched it stores potential energy. When the arrow is released the potential energy stored in the bow gets transformed into the kinetic energy of the arrow.
(b) Given m = 50 kg, h = 100 m,
g = 10 ms–1, PE = ?
PE = mgh = 50 × 10 × 100 = 5000 J

Question. Give an example of potential energy due to change in shape.
Ans : A stretched bow has potential energy due to change of shape.

Question. What type of energy is possessed by a flying bird and a flying aeroplane?
Ans : Both potential energy and kinetic energy.

Question. When do we say that work is done?
Ans : Work is said to be done when a force causes displacement of an object in the direction of applied force.

Question. Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Ans : Work done = Force × Displacement

Question. Define : (a) power (b) work done (c) kinetic energy.
Give SI unit of each.
Ans : (a) The rate of doing work is called power. Its SI unit is watt.
(b) Work is the product of force and displacement. Its SI unit is joule.
(c) It is the energy possessed by a body by virtue of its motion. Its SI unit is joule.

Question. Find the energy in kWh consumed in 10 hours by a machine of power 500 W.
Ans :
W = P × t
= 500 × 10 = 5000 Wh = 5 kWh.

Question. When is work said to be done against the force of gravity?
Ans :
When a body is lifted, the work is done against the force of gravity.

Question. Calculate the cost of using a 2 kWh immersion rod for heating water in a house for one hour each day for 60 days if the rate is 1.50 per unit kWh.
Ans : E = Pt = 2 kW × 60 × 1 h
= 120 kWh = 120 unit
The cost of using a 2 kWh immersion rod for heating
water = 120 × 1.5 = Rs 180

Question. A work of 4900 J is done on load of mass 50 kg to lift it to a certain height. Calculate the height through which the load is lifted.
Ans : Work done on road to lift = mgh
4900 = 50 × 9.8 h
h=10m

Question. What is the SI unit of work done and power?
Ans : Joule and Watt.

Question. When is 1 joule of work said to be done?
Ans : When a force of 1 newton acting on a body displaces it 1m in its own direction.

Question. Does work done depend upon the velocity of the body.
Ans : No.

Question. State the law of conservation of energy.
Ans : It states that energy can neither be created nor destroyed. It can only change its form.

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### CBSE Class 9 Science Chapter 11 Work And Energy Assignment

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#### Assignment for Science CBSE Class 9 Chapter 11 Work And Energy

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#### Chapter 11 Work And Energy Assignment Science CBSE Class 9

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#### Chapter 11 Work And Energy Assignment CBSE Class 9 Science

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#### CBSE Science Class 9 Chapter 11 Work And Energy Assignment

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