#### 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.

#### Solution 1

(a), (b)

**(a) **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.

**(b) **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.

**(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.

#### Solution 2

a) The railway carriage moving without jerks between two stations, so the distance between two stations is considered to be large as compared to the size of the train. Therefore the train is considered as a point object.

(b) The monkey may be considered as point object because value of distance covered on a circular track is much greater.

(c) As turning of ball is not smooth, thus the distance covered by ball is not large in the reasonable time. Therefore ball cannot be considered as point object.

(d) Again a tumbling beaker slipped off the edge of a table cannot be considered as a point object because distance covered is not much larger.