Frank Solutions for Chapter 1.5 Different Forms, Conservation and Transformation of Energy Class 10 Physics ICSE
Exercise
1. Define kinetic energy.
Answer
The energy possessed by a body by virtue of its motion is called kinetic energy.
2. Give two examples of kinetic energy.
Answer
Examples of kinetic energy:
(i) Air in motion has kinetic energy.
(ii) A swinging pendulum
(i) Air in motion has kinetic energy.
(ii) A swinging pendulum
3. Write the SI units of energy.
Answer
SI unit of energy is 'joule'.
4. Name the physical quantity which is equal to the energy of a body.
Answer
Work
5. Name the physical quantity which is associated with the work done by a body.
Answer
'Energy' is the body's ability to do work.
6. Is kinetic energy a scalar or a vector physical quantity?
Answer
Energy is a scalar quantity.
7. If the speed of a body is doubled, what happens to its kinetic energy?
Answer
8. What are the physical parameters on which the kinetic energy of a body depends?
Answer
Kinetic energy of a body depends upon:
- Mass of the body
- Speed of the body
9. Can a body possess zero kinetic energy?
Answer
Yes, if the body is not in motion; it has zero kinetic energy
10. Name the type of energy possessed by a moving bullet.
Answer
A moving bullet possesses kinetic energy
11. A body of mass 2 kg is moving with a speed of 20 ms-1. What is its K.E.?
Answer
or, K.E. = 400 J
Thus, K.E. is 400 J
12. A moving object of mass 30 kg has 60 J of kinetic energy. What is its speed?
Answer
13. What type of energy is possessed by a flowing water?
Answer
Flowing water possesses kinetic energy.
14. If the speed of a particle is increased four times, how will its kinetic energy be affected?
Answer
15. A bus and a car have the same K.E. which of the two should be moving faster? Explain.
Answer
The car should be moving faster because the mass of the car is less than that of the bus.
16. A body is thrown vertically upwards. Its velocity keeps on changing. What happens to its K.E. when does its velocity become zero?
Answer
Its kinetic energy changes with the change in velocity.
Velocity becomes zero at the highest point.
Velocity becomes zero at the highest point.
17. What change should be effected in the velocity of a body to maintain the same K.E., if its mass is increased four times?
Answer
18. The K.E. of a body is 5 J. What will be its K.E. when its speed is doubled?
Answer
Thus, K.E. becomes four times.
Thus, if initially the K.E. is 5 J, after increasing the speed twice, its K.E. will become 4 × 5 = 20 J.
19. Name the parameters that can change the K.E.
Answer
The parameters that can change the kinetic energy are:
- Mass
- Speed
20. Give an example of a body possessing no K.E.
Answer
A ball at lying at rest on the floor possesses zero kinetic energy.
21. Define potential energy.
Answer
The energy possessed by a body by virtue of its position, shape or change of configuration is called potential energy.
22. What are the factors on which P.E. of a body depends?
Answer
Potential energy of a body depends upon:
- Mass of the body
- Acceleration due to gravity
- Height of the body
23. What is the amount of energy spent in lifting 1 kg through 1 m? Take g = 10 ms-2.
Answer
P.E. = mgh = 1×10 ×1 = 10 J
24. Give two examples of P.E.
Answer
Examples of potential energy:
- Water stored at a height in a reservoir.
- A stretched spring.
25. What is the P.E. of a body lying on the surface of the earth?
Answer
P.E of a body lying on a floor is zero.
26. What is the amount of energy spent by the heart in pumping blood through the body?
Answer
The energy spent by the heart in pumping blood through the body is 1 J per beat.
27. Name the type of energy possessed by a body due to a change in configuration.
Answer
Potential energy
28. How is energy stored in a clock?
Answer
The work done in winding a clock spring is stored as P.E. in the spring. This P.E. is then used to run the hands of the clock.
29. What is the P.E. of a body of mass M at a height H above the earth's surface?
Answer
P.E. of a body of mass M and at a height H above the earth's surface is:
P.E. = MgH ; here, g = acceleration due to gravity.
P.E. = MgH ; here, g = acceleration due to gravity.
30. Is P.E. a vector or a scalar quantity?
Answer
P.E. is a scalar quantity.
31. Name the type of energy possessed by a
(i) stretched catapult
(ii) hot iron
(iii) wound up clock
(iii) wound up clock
Answer
(i) Potential energy
(ii) Heat energy
(iii) Potential energy
(ii) Heat energy
(iii) Potential energy
32. An object is dropped from a height H. when is its
(a) P.E. maximum,
(b) K.E. maximum,
(c) P.E. = K.E.?
(b) K.E. maximum,
(c) P.E. = K.E.?
Answer
(a) At the height H because the height is maximum.
(b) At the ground level because the velocity is maximum.
(c) At half distance of the total path i.e. at height H/2, the P.E. is equal to the K.E.
(b) At the ground level because the velocity is maximum.
(c) At half distance of the total path i.e. at height H/2, the P.E. is equal to the K.E.
33. A cricket ball is thrown up from the earth's surface. What happens to its P.E.
(a) during the motion
(b) at the highest point?
(b) at the highest point?
Answer
(a) As the height above the ground increases, the potential energy also increases.
(b) At the highest point, the height of the cricket ball is maximum and hence the potential energy is also maximum.
(b) At the highest point, the height of the cricket ball is maximum and hence the potential energy is also maximum.
34. What is the difference between K.E. and P.E.?
Answer
P.E. is the energy possessed by a body by virtue of its position, shape or configuration but K.E. is the energy possessed by a body by virtue of its velocity or motion.
E.g. A ball kept on a cliff possesses P.E. but as soon as it is kicked it possesses K.E.
E.g. A ball kept on a cliff possesses P.E. but as soon as it is kicked it possesses K.E.
35. What is meant by the transformation of energy?
Answer
Whenever one form of energy dissipates or disappears, another form of equivalent amount of energy is produced; this is referred to as transformation of energy.
E.g. when a particular switch is pressed electric lamps light up owing to the heat produced in the filament. This is the transformation of electrical energy to heat and light energy.
E.g. when a particular switch is pressed electric lamps light up owing to the heat produced in the filament. This is the transformation of electrical energy to heat and light energy.
36. Does the total energy of a body always remain constant?
Answer
No, total energy of a body does not remain constant but the total energy of a closed system remains constant e.g. universe.
37. Is energy a scalar or a vector physical quantity?
Answer
Energy is a scalar quantity.
38. Can we destroy every energy associated with a body?
Answer
No, we cannot destroy energy associated with a body.
39. Define energy of a body.
Answer
Energy is the capacity or ability of a body to do work or energy is stored work.
40. State the law of conservation of energy.
Answer
The law of conservation of energy states that energy cannot be created or destroyed; the sum total of energy in a closed system remains unchanged. Energy only changes from one form to another.
41. A dry cell converts one form of energy into another. Name the two forms.
Answer
A dry cell converts chemical energy into electrical energy.
42. Name the device that converts electrical energy into mechanical energy.
Answer
A D.C. motor converts electrical energy into mechanical energy.
43. Name the device that converts mechanical energy into electrical energy.
Answer
A dynamo converts mechanical energy into electrical energy.
44. Name four different forms of energy.
Answer
Four different forms of energy:
(i) Solar energy
(ii) Mechanical energy
(iii) Wind energy
(iv) Nuclear energy
(i) Solar energy
(ii) Mechanical energy
(iii) Wind energy
(iv) Nuclear energy
45. What kind of energy transformation takes place at a thermal power station?
Answer
At a thermal power station, nuclear energy is converted into electrical energy.
46. Name the energy changes for each of the following cases:
(i) electric ball
(ii) bicycle brakes
(iii) pendulum
(iv) human body
(v) dynamo
(ii) bicycle brakes
(iii) pendulum
(iv) human body
(v) dynamo
Answer
(i) Electrical energy to sound energy
(ii) Mechanical energy into heat energy.
(iii) Potential energy into kinetic energy and vice-versa.
(iv) Chemical energy obtained from food is converted into mechanical energy and heat energy in muscles.
(v) A dynamo converts mechanical energy into electrical energy.
(ii) Mechanical energy into heat energy.
(iii) Potential energy into kinetic energy and vice-versa.
(iv) Chemical energy obtained from food is converted into mechanical energy and heat energy in muscles.
(v) A dynamo converts mechanical energy into electrical energy.
47. What is meant by power?
Answer
The rate of doing work is called power.
48. Write the SI units of power.
Answer
'Watt' is the SI unit of power.
49. Define one horse power.
Answer
Horse power is the unit of power. The horsepower used for electrical machines is defined as exactly 746 watt.
Classically, a horse exerting 1 H.P. can raise 330 pounds of coal 100 feet in a minutes, or 33 pounds of coal 1,000 feet in one minute, or, 1,000 pounds 33 feet in one minute.
Classically, a horse exerting 1 H.P. can raise 330 pounds of coal 100 feet in a minutes, or 33 pounds of coal 1,000 feet in one minute, or, 1,000 pounds 33 feet in one minute.
50. Define the unit 'watt'. How is it related to horse power?
Answer
If 1 joule of work is done in 1 second, the power is said to be 1 watt.
1 H.P. = 746 watt
1 H.P. = 746 watt
51. A body does 20 J of work in 10 s. What is its power?
Answer
Power = work done/time taken = 20/10 = 2 watt
52. Name the physical quantity associated with the 'rate of doing work'.
Answer
Power is the physical quantity associated with the 'rate of doing work'.
53. An electric motor drives a machine which lifts a mass of 4 kg through a height of 10 m in 5 s at a constant speed. Assuming g = 10 ms-2, calculate
(i) the amount of work done,
(ii) the power of the machine.
Answer
Given, mass m = 4 kg, height h = 10 m, time t = 5 s
(i) work done = mgh = 4×10 × 10 = 400 J
(ii) power = work done/time taken = 400/5 = 80 W
(i) work done = mgh = 4×10 × 10 = 400 J
(ii) power = work done/time taken = 400/5 = 80 W
54. Name the practical unit of power.
Answer
Practical or commercial unit of power is kilowatt-hour.
55. In what form is energy stored in a wrist watch?
Answer
When we wind a watch, the configuration of its spring is changed. The energy stored in the spring is obviously potential in nature (elastic potential to be more accurate).
56. A log of wood cut by a saw becomes hot. From where does this heat energy come?
Answer
This heat energy comes from the mechanical energy.
57. Our hands become warm when we rub them against each other. Why?
Answer
When we rub our hands, mechanical energy is converted into heat energy.
58. The head of a nail becomes warm when it is hammered into a plank of wood. Explain the series of energy transformation taking place in the process.
Answer
When the head of a nail is struck with a hammer, the mechanical energy of the hammer pushes the nail into the plank of wood and in this process a part of energy is converted into heat energy.
59. A 100 W electric lamp emits energy in the form of light at the rate 10 J per second. What percentage of electric energy does the lamp transform into light energy?
Answer
Given, power of lamp = 100 watt
Rate of dissipation of light = 10 j/s
Therefore, percentage of electrical energy converted into light energy =(10/100) ×100% = 10%
Rate of dissipation of light = 10 j/s
Therefore, percentage of electrical energy converted into light energy =(10/100) ×100% = 10%
60. A horse exerts a pull on a cart of 300 N so that the horse-cart system moves with a uniform speed 18 km/h on a level road. Calculate the power developed by the horse in watt and also find its equivalent in horse power.
Answer
61. If an electric bulb of 100 watt is lighted for 2 hours, how much electric energy would be consumed?
Answer
Given, Power = 100 watt, time = 2 hrs
Energy consumed = power × time
= 100×2×60×60
= 7.2 ×105 J
62. A woman pulls a bucket of water of total mass 5 kg from a well which is 10 s. calculate the power used by her.
Answer
Given, mass = 5 kg, height = 10 m, time = 10s
Power = mgh/t = (5×10×10)/10 = 50 watt