Question:
Two bodies of equal masses move with uniform velocities v and 3 v respectively.Find the ratio of their kinetic energies.
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.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 5.
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 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.
How does the wind move the blades of a wind-mill ?
Q 8.
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 9.
What is the form of energy possessed by a running car?
Q 10.
What do the machines need for their working ?
Q 11.
Name two forms of mechanical energy.
Q 12.
When is work done by a force zero ?
Q 13.
Why do some engines require fuels like petrol and diesel ?
Q 14.
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 15.
Name the device which converts electrical energy into mechanical energy.
Q 16.
Fill in the blanks :
Ability to do work is called _______.
Q 17.
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 18.
Name the type of energy possessed by a raised hammer?
Q 19.
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 20.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 21.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 22.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 23.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 24.
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 25.
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 26.
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 27.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Q 28.
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 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.
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 31.
Define average power.
Q 32.
Is a person doing any work by holding a suitcase ?
Q 33.
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 34.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 35.
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 36.
Can a body have energy without having momentum ?
Q 37.
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 38.
How is energy stored in a clock ?
Q 39.
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 40.
A heavy stone is lowered to the ground with the help of rope. Is the work done by the applied force positive or negative?
Q 41.
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 42.
What is Kilowatt hour?
Q 43.
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 44.
Is work a scalar quantity or a vector quantity ?
Q 45.
Name a few forms of energy and their transformation into each other.
Q 46.
In physics,energy is an indirectly observed quantity that is often understood as the ability of a physical system to do work on other physical systems.However,this must be understood as an overly simplified definition as we shall come to know in higher classes that not all energy can perform work.
(a) How did the concept of energy emerge ?
(b) How much electric energy is generated in a typical lightning strike ? What are the forms to which this energy gets converted ?
(c) What is the kinetic energy of a passenger seated in a moving plane :(i) with respect to the plane (ii) with respect to the Earth.
Q 47.
When do we say that work is done?
Q 48.
A boy of mass 45 kg climbs up 20 steps in 20 second. If each step is 25 cm high, calculate the power used in climbing
Q 49.
Fill in the blanks :
Work is a ______ (scalar/vector) quantity.
Q 50.
Fill in the blanks :
Work done against gravity in lifting a mass is stored as ______. Numerically, it is equal to m ×_ ×__.
