Question 1

Question 1Write true or false for each statement:(a) A man going up has potential energy and kinetic energy both.(b) A gum bottle lying on a table has no energy.(c) In an electric fan, electrical energy changes into mechanical energy.(d) Potential energy changes into kinetic energy when it is put to use.(e) One form of energy cannot be converted into another form.(f) There is always some loss of energy in conversion from one form of energy to another form, so the total energy is not conserved.(g) The energy of flowing water can be converted into electric energy (electricity).

Accepted Answer

(a) True(b) FalseCorrect Statement — A gum bottle lying on a table has potential energy.(c) True(d) True(e) FalseCorrect Statement — One form of energy can be converted into another form.(f) FalseCorrect Statement — The total energy is always conserved in each transformation of energy.(g) True

Question 2

Question 3Match the following:Column AColumn B(a) Running water(i) heat energy(b) Burning(ii) vibrations(c) Energy(iii) atom bomb(d) Sound energy(iv) kinetic energy(e) Nuclear energy(v) joule

Accepted Answer

Column AColumn B(a) Running water(iv) kinetic energy(b) Burning(i) heat energy(c) Energy(v) joule(d) Sound energy(ii) vibrations(e) Nuclear energy(iii) atom bomb

Question 3

Question 4aSelect the correct alternative:When we rub our handskinetic energy changes into potential energymechanical energy changes into heat energypotential energy changes into kinetic energyheat energy changes into mechanical energy

Accepted Answer

mechanical energy changes into heat energyReason — When we rub our hands we feel heat i.e. mechanical energy changes into heat energy.

Question 4

Question 2State the unit of energy and define it?

Accepted Answer

The S.I. unit of energy is joule(J).A body is said to possess an energy of one joule if one joule work is done to bring the body in that state i.e. a force of 1 newton moves the body by a distance of 1 metre in the direction of force.

Question 5

Question 5What is potential energy? State its unit.

Accepted Answer

Potential energy of a body is the energy possessed by it due to its state of rest or position. It is equal to the work done in bringing the body to that state of rest or position. Its unit is joule(J).

Question 6

Question 6Give one example of a body that has potential energy, in each of the following:(i) due to its position(ii) due to its state

Accepted Answer

(i) A hammer at a height has potential energy stored in it because of its position at a height.(ii) A wound up watch spring has potential energy because of the wound up state of its coils.

Question 7

Question 7State two factors on which the potential energy of a body at a certain height above the ground depends.

Accepted Answer

The two factors on which the potential energy of a body at a certain height above the ground depends are:Mass of the body — Greater the mass of the body, greater is the potential energy of the body.Its height above the ground — Higher the height of the body above the ground, more is the potential energy.

Question 8

Question 8Two bodies A and B of masses 10 kg and 20 kg respectively are at the same height above the ground. Which of the two has greater potential energy?

Accepted Answer

Body B has greater potential energy.Reason — Both bodies, A and B are at the same height above the ground. Value of g is also same for both. As the mass of body B (20 kg) is greater than that of body A (10 kg) hence potential energy of body B is greater.

Question 9

Question 9A bucket full of water is on the first floor of your house and another identical bucket with same quantity of water is kept on the second floor. Which of the two has greater potential energy?

Accepted Answer

The bucket kept on second floor has greater potential energy.Reason — The two buckets are identical containing the same amount of water so their mass is same. Value of g is also same for the two buckets. As the bucket on second floor is at a greater height hence its potential energy is also greater.

Question 10

Question 10Define the term kinetic energy. Give one example of a body which possesses kinetic energy.

Accepted Answer

Kinetic energy of a body is the energy possessed by it due to its state of motion. Example: A fast moving stone has kinetic energy which has the capacity of breaking a window pane when it strikes on it.

Question 11

Question 11State two factors on which the kinetic energy of a moving body depends.

Accepted Answer

The two factors on which the kinetic energy of a moving body depends are:The mass of the body — Greater the mass of the body, higher is its kinetic energy.The speed of the body — More the speed of the body, higher is its kinetic energy.

Question 12

Question 12Two toy cars A and B of masses 500 g and 200 g respectively are moving with the same speed. Which of the two has greater kinetic energy?

Accepted Answer

The toy car A has greater kinetic energy than toy car B.Reason — The two toy cars A and B are moving with the same speed. As the toy car A has greater mass (500 g) than toy car B (200 g) hence its kinetic energy is also greater.

Question 13

Question 13A cyclist doubles his speed. How will his kinetic energy change: increases, decreases or remains the same?

Accepted Answer

Kinetic energy of cyclist will increase as speed is doubled because more the speed of the body, more is its kinetic energy.

Question 14

Question 14Name the form of energy which a wound up watch spring possesses.

Accepted Answer

Potential Energy.

Question 15

Question 15Can a body possess energy even when it is not in motion? Explain your answer with an example.

Accepted Answer

Yes, a body can possess energy even when it is not in motion.Example — A stone at rest placed at a height above the ground has potential energy. Even though the body is not in motion (kinetic energy = 0), but when a body is raised to a height say h possess potential energy because of its raised position.

Question 16

Question 16Name the type of energy (kinetic or potential) possessed by the following:(i) A moving cricket ball.(ii) A stone at rest on the top of a building.(iii) A compressed spring.(iv) A moving bus.(v) A bullet fired from a gun.(vi) Water flowing in a river.(vii) A stretched rubber band.

Accepted Answer

(i) A moving cricket ball has kinetic energy due to its state of motion.(ii) A stone at rest on the top of a building has potential energy due to its raised position.(iii) A compressed spring has potential energy due to its compressed state.(iv) A moving bus has kinetic energy due to its state of motion.(v) A bullet fired from a gun has kinetic energy due to its state of motion.(vi) Water flowing in a river has kinetic energy due to its state of motion.(vii) A stretched rubber band has potential energy because of its stretched position.

Question 17

Question 17Give one example to show the conversion of potential energy to kinetic energy when put in use.

Accepted Answer

A stone placed at a top of building has potential energy due to its height and when it is dropped from the top of the building it begins to fall. When it begins to fall the potential energy stored in it changes into kinetic energy. So the falling stone has kinetic energy.

Question 18

Question 18State the energy changes that occur in the following:(i) The unwinding of a watch spring.(ii) Burning coal while operating a steam engine(iii) Lighting of a torch bulb.(iv) An electric generator (or dynamo).

Accepted Answer

(i) During the unwinding of a watch spring, the potential energy changes into kinetic energy.(ii) In a steam engine chemical energy of coal first changes into heat energy which is transferred to steam. Then the heat energy of steam changes into mechanical energy which causes the train to move.(iii) When torch bulb is lighted, chemical energy of batteries change into light and heat energy.(iv) In an electric generator (dynamo) mechanical energy changes into electrical energy.

Question 19

Question 19Energy can exist in several forms and may change from one form to another. Give two examples to show the conversion of energy from one form to another.

Accepted Answer

The two examples that show the conversion of energy from one form to another are:In an electric fan, the electrical energy changes into mechanical energy that rotates the blades of a fan.In a glowing bulb, the electrical energy changes into heat energy and light energy.

Question 20

Question 20Give one relevant example for each of the following transformations of energy:(i) Electrical energy to heat energy(ii) Electrical energy to mechanical energy(iii) Electrical energy to light energy(iv) Chemical energy to heat energy(v) Chemical energy to light energy

Accepted Answer

(i) Electric iron(ii) Electric motor(iii) Glowing bulb(iv) Burning of wood(v) Bursting of crackers

Energy

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