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.

(A, B) The size of a railway carriage is very small compared to the distance between two stations. Therefore,the carriage can be treated as a point-sized object.
$(b)$ The size of a monkey is very small compared to the size of a circular track. Therefore,the monkey can be considered as a point-sized object on the track.
$(c)$ 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.
$(d)$ 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.