Question

In which of the following examples of motion, can the body be considered approximately a point object:

(a) A railway carriage moving without jerks between two stations.
(b) A monkey sitting on top of a man cycling smoothly on a circular track.
(c) A spinning cricket ball that turns sharply on hitting the ground.
(d) A tumbling beaker that has slipped off the edge of a table.

Answer 1

(a), (b)
The size of a carriage is very small as compared to the distance between two stations. Therefore, the carriage can be treated as a point sized object.
The size of a monkey is very small as compared to the size of a circular track. Therefore, the monkey can be considered as a point sized object on the track.
The size of a spinning cricket ball is comparable to the distance through which it turns sharply on hitting the ground. Hence, the cricket ball cannot be considered as a point object.
The size of a beaker is comparable to the height of the table from which it slipped. Hence, the beaker cannot be considered as a point object.