Selina solutions concise physics class 7 icse Solutions for Chapter 3 energy

Exercises in Chapter 3 energy Grade 7

Objective Questions

Short/Long Answer Questions

Questions in Objective Questions

Q1) Write 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.

(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 .

Q2) Fill in the blanks

(a) An electric fan converts electrical energy into ________ energy .

(b) Cooking gas converts ________ energy into heat energy.

(d) The ability to do work is called ________ .

(e) The energy possessed by a body due to its position is called ________ energy.

(f) The energy possessed by a body due to its movement is called ________ energy

(g) Green plants convert ________ energy into chemical energy.

(h) The S.I. The unit of energy is ________ .

(i) An object falling freely from the roof of a multistorey building has ________ and ________ energy when halfway down a building.

Q3) Match the following:

Column A	Column B
(a) running water	(i) energy
(b) burning	(ii) vibrations
(c) energy	(iii) atom bomb
(d) sound energy	(iv) kinetic energy
(e) nuclear energy	(v) joule

Q4) Select the correct alternative: (a) When we rub our hands

kinetic energy changes into potential energy
mechanical energy changes into heat energy
potential energy changes into kinetic energy
heat energy changes into mechanical energy.

(b) A ball rolling on the ground possesses

kinectic energy
potential energy
no energy
heat energy

chemical energy
electrical energy
heat energy
mechanical energy

(d) When a bulb lights up on passing current, the change of energy is

from electrical energy to heat energy
from electrical energy to light energy
from electrical energy to heat and light energy
from electrical energy to mechanical energy

(e) The correct statement is

Both work and energy have the same units.
Potential energy of a body is due to its motion.
Kinetic energy of a body is due to its position or state.
Kinetic energy can change into potential energy , but potential energy cannot change into kinetic energy.

(f) According to law of conservation of energy, energy changes from one form to another form, but the total energy of that system

increases
decreases
alternates
remains the same

Questions in Short/Long Answer Questions

Q1) Define the term energy.

Q2) State the unit of energy and define it.

Q3) Name the different forms of energy .

Q4) What are the two kinds of mechanical energy ?

Q5) What is potential energy? State its unit.

Q6) Give one example of a body that has potential energy, in each of the following : (i) due to its position, (ii) due to its state.

Q7) State two factors on which the potential energy of a body at a certain height above the ground depends.

Q8) Two bodies A and B of masses 10kg and 20kg respectively are at the same height above the ground. Which of the two has the greater potential energy?

Q9) A bucket full of water is on the first floor of your house and another identical bucket with the same quantity of water is kept on the second floor. Which of the two has greater potential energy?

Q10) Define the term kinetic energy. Give one example of a body which possesses kinetic energy.

Q11) State two factors on which the kinetic energy of a moving body depends.

Q12) Two toy-car A and B of masses 500g and 200g respectively are moving at the same speed. Which of the two has the greater kinetic energy?

Q13) A cyclist doubles his speed. How will his kinetic energy change: increases; decreases or remain same ?

Q14) Name the form of energy which a wound up watch spring possess.

Q15) Can a body possess energy even when it is not in motion? Explain your answer with an example .

Q16) Name 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 the 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

Q17) Give one example to show the conversion of potential energy to kinetic energy when put in use.

Q18) State 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).

Q19) Energy 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.

Q20) Give one relevant example for each of the following transformation 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.

Q22) Give one example to show that the sum of potential energy and kinetic energy remains constant if friction is ignored.

Q23) A ball is made to fall freely from a height. State the kind/ kinds of energy possessed by the ball when it is (a) at the highest point (b) just in the middle (c) at the ground

Q24) State the changes in form of energy while producing hydro electricity.