Answer:
When the force applied or the displacement is zero or when both are perpendicular to each other, zero work is done.
Mathematically,
Work and Energy
Q 1.
A body is thrown vertically upwards. Its velocity goes on decreasing. Write the change in kinetic energy when its velocity becomes zero.
Q 2.
Name a machine that transforms muscular energy into useful mechanical work.
Q 3.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 4.
Define potential energy.Derive an expression for the potential energy of a body of mass m,at a height h above the surface of the Earth.
Q 5.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 6.
Two girls,each of weight 400 N,climb up a rope through a height of 8 m.We name one of the girls A and the other B.Girl A takes 20 s while B takes 50 s to accomplish this task.What is the power expended by each girl ?
Q 7.
How does the wind move the blades of a wind-mill ?
Q 8.
What do the machines need for their working ?
Q 9.
What is the form of energy possessed by a running car?
Q 10.
An object of mass 15 kg is moving with a uniform velocity of 4 m/s.What is the kinetic energy possessed by the object ?
Q 11.
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?
Q 12.
Name two forms of mechanical energy.
Q 13.
Name the device which converts electrical energy into mechanical energy.
Q 14.
When is work done by a force zero ?
Q 15.
Why do some engines require fuels like petrol and diesel ?
Q 16.
A boy of mass 55 kg runs up a flight of 40 stairs,each measuring 0.15 m.Calculate the work done by the boy
Q 17.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 18.
Name the type of energy possessed by a raised hammer?
Q 19.
A porter lifts a luggage of 15 kg from the ground and puts it on his head 1.5 m above the ground.Calculate the work done by him on the luggage.
Q 20.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 21.
Fill in the blanks :
Ability to do work is called _______.
Q 22.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 23.
A force of 7 N acts on an object.The displacement is,say 8 m,in the direction of the force,[in Fig.].Let us take it that the force acts on the object throughout the displacement What is the work done in this case ?
Q 24.
The velocity of a body moving in a straight line is increased by applying a constant force F,for some distance in the direction of the motion. Prove that the increase in the kinetic energy of the body is equal to the work done by the force on the body.
Q 25.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 26.
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.
Q 27.
The mass of a ball A is double the mass of another ball B.The ball A moves at half the speed of the ball B.Calculate the ratio of the kinetic energy of A to the kinetic energy of B.
Q 28.
A boy of mass 50 kg runs up a staircase of 45 steps in 9 s.If the height of each step is 15 cm,find his power.Take g =
.
Q 29.
Define average power.
Q 30.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Q 31.
Is a person doing any work by holding a suitcase ?
Q 32.
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?
Q 33.
Fill in the blanks :
A force acting on a body shows a displacement in the direction of the force. It is said _______ is done on the body.
Q 34.
What is mechanical energy? What are its types?
Q 35.
A body of mass 120 g is taken vertically upwards to reach the height of 5m. Calculate work done. (Take g = 10 m/s
2)
Q 36.
A bullet of mass 20 g is found to pass two points 30 m apart in 4 s ? Assuming the -speed to be constant,find its kinetic energy.
Q 37.
Is work a scalar quantity or a vector quantity ?
Q 38.
Give examples for the following scenarios of energy transformations. You may choose the answer(s) from the following list of words
solar cell, turbine, mixer, fan, steam engine, automobiles, green plants, nuclear reactor, electric bulb, torch, electric bulb, microphone, loudspeaker, geyser, heater, car battery, inverter, LPG
| SNo. |
Energy Transformation
From ⟶ To |
Give Example |
| 1. |
Mechanical ⟶ Electrical |
_________ |
| 2. |
Electrical ⟶ Mechanical |
_________ |
| 3. |
Electrical ⟶ Heat |
_________ |
| 4. |
Heat ⟶ Mechanical |
_________ |
| 5. |
Electrical ⟶ Light |
_________ |
| 6. |
Electrical ⟶ Sound |
_________
|
| 7. |
Chemical ⟶ Heat |
_________ |
| 8. |
Electrical ⟶ Chemical |
_________ |
| 9. |
Sound ⟶ Electrical |
_________ |
| 10. |
Chemical ⟶ Electrical |
_________ |
| 11. |
Light ⟶ Electric |
_________ |
| 12. |
Chemical ⟶ Mechanical |
_________ |
| 13. |
Nuclear ⟶ Electrical |
_________ |
| 14. |
Light ⟶ Chemical |
_________ |
Q 39.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 40.
A momentum of the body is increased by 20%. What is the percentage increase in its kinetic energy?
Q 41.
A coolie carries a load of 50 kg on his head and walks on a level road upto 100 m.What is the work done by him ?
Q 42.
A man does 200 J of work in 10 s and a boy does 100 J of work in 4 s.(a) Who is delivering more power ?
(b) Find the ratio of the power delivered by the man to that delivered by the boy.
Q 43.
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 objjgft by the gravitational force ? Explain your answer.
Q 44.
How is energy stored in a clock ?
Q 45.
What is the difference between potential energy and kinetic energy ?
Q 46.
What do you mean by work ?Give its scientific conception.
Q 47.
Define 1 J of work.
Q 48.
Name a few forms of energy and their transformation into each other.
Q 49.
Can a body have energy without having momentum ?
Q 50.
Fill in the blanks :
A stretched rubber band acquires _________(potential/kinetic) energy.
