(i) A metal rod AB of length 80 cm is balanced at 45 cm from the end A with 100 gf weights suspended from the two ends.
(a) If this rod is cut at the centre C, then compare the weight of AC to the weight of BC. (b) Give a reason for your answer in (a)


(ii) For each of the following scenarios, state whether the work done by gravity is positive, negative, or zero.
(a) a person walks on a levelled road.
(b) a person climbs a ladder.
(c) a car in neutral gear is coming down the slope.

(iii) The figure below shows a simple pendulum of mass 200 g. It is displaced from the mean position A to the extreme position B. The potential energy at the position A is zero. At the position B the pendulum bob is raised by 5 m.


(a) What is the potential energy of the pendulum at the position B?
(b) What is the total mechanical energy at point C?
(c) What is the speed of the bob at the position A when released from B?
(Take g = 10 ms² and given that there is no loss of energy.)

Solution

,,