Question:
Fill in the blanks :
Work done on an object is _____ if displacement is zero.
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.
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 5.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 6.
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 7.
What do the machines need for their working ?
Q 8.
How does the wind move the blades of a wind-mill ?
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.
Name two forms of mechanical energy.
Q 12.
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 13.
When is work done by a force zero ?
Q 14.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 15.
Name the device which converts electrical energy into mechanical energy.
Q 16.
Why do some engines require fuels like petrol and diesel ?
Q 17.
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 18.
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 19.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 20.
Name the type of energy possessed by a raised hammer?
Q 21.
Fill in the blanks :
Ability to do work is called _______.
Q 22.
Define average power.
Q 23.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 24.
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 25.
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 26.
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 27.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 28.
Can a body have energy without having momentum ?
Q 29.
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 30.
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 31.
Two friends Ram and Shyam, each having weight of 40 kg, go for rock climbing. Ram climbs to a height of 3 m in 10 s. and Shyam covers the same height in 12 s. Is the work done by Ram and Shyam equal ? or not ? Compare the power of Ram and Shyam.
Q 32.
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 33.
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 34.
Give an example where potential energy is acquired by a body due to change of its shape.
Q 35.
Name a few forms of energy and their transformation into each other.
Q 36.
A bullet of mass 0.03 kg moving with a speed of 400 m/s penetrates 12 cm into fixed block of wood.Calculate the average force exerted by the wood on the bullet.
Q 37.
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 38.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Q 39.
Is work a scalar quantity or a vector quantity ?
Q 40.
Is a person doing any work by holding a suitcase ?
Q 41.
When do we say that work is done?
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 object by the gravitational force? Explain your answer.
Q 44.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 45.
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 46.
A momentum of the body is increased by 20%. What is the percentage increase in its kinetic energy?
Q 47.
Calculate the power of an engine required to lift 105 kg of coal per hour from a mine 360 m deep.
Q 48.
The global climate has always fluctuated.Millions of years ago,some parts of the world that are now quite warm, were covered with ice,and over recent centuries,average temperatures have risen and fallen in cycles.What is new,however,is that current and future climate change will be caused not just by natural events but also by activities of human beings.Suggest three simple ways to help save the climate of our planet.
Q 50.
Two bodies of masses m
1 and m
2 have equal kinetic energies. If p
1 and p
2 are their respective momentum, then ratio p
1 : p
2 is ___?
