Q3 of 33 Page 158

A battery lights a bulb. Describe the energy changes involved in the process.

Within the electric cell of the battery the chemical energy changes into electrical energy. The electric

Energy on flowing through the filament of the bulb, first changes into heat energy and then into the light energy


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1

Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term ‘work’:

(a) Suma is swimming in a pong.


(b) A donkey is carrying load on its back.


(c) A wind-mill is lifting water from a well.


(d) A green plant is carrying out photosynthesis.


(e) An engine is pulling a train.


(f) Food-grains are getting dried in the sun.


(g) A sailboat is moving due to wind energy.

 2

An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?

 4

Certain force acting on a 20 kg mass changes its velocity from 5 m s-1 to 2 m s-1. Calculate the work done by the force.

 5

An object of mass 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.