Explain why it is desirable to install an air conditioner near the ceiling of a room and not close to the floor.

 (a) On what principle does lighting in a fluorescent tube operate?

(b) State two factors which determine the colour of light produced in a fluorescent tube.

The diagram above illustrates an arrangement of a cathode ray from an electron gun and a bar magnet placed perpendicularly to the direction of the ray. Will the ray bend downward or upward? Explain.

 (a) Explain wave-particle duality of light.

(b) Illustrate your answer in (a) with observable phenomena.

(a) State the principle of conservation of linear momentum.

(b) Explain the mode of action of a propelled rocket.

(c) During a training session, two footballers pass a ball repeatedly between themselves. Give two reasons why the to and fro motion of the ball is not simple harmonic.

(d) A ball is dropped from a height, at the same time as another ball is projected horizontally from the same height.

(i) Would the balls hit the ground at the same time?

(ii) Explain your answer in (i).

(e) A ball of mass 0.10 kg is projected horizontally onto a vertical wall with a speed of 17 ms\(^{-1}\). The ball makes contact with the wall for 0.15 s and rebounds horizontally with a speed of 13 ms\(^{-1}\).

Calculate the:

(i) change in momentum of the ball;

(ii) average force exerted on the ball during its collision with the wall.