Point Mass Object
When an object in motion covers a very large distance as compared to its size or dimensions, then to study the motion of that object, its size or dimensions can be neglected and object can be regarded as a point object.
Thus, an object can be considered as a point object if during motion in a given time, it covers distances much greater than its own size. In the above figure car can be considered as a point object as it covers a very long distance as compared to its length.
For example, while studying the revolution of earth around the sun, the diameter of earth being very small as compared to the length of its orbit around the sun, the earth can be regarded as a point object.
Similarly, a car travelling a few hundred kilometer distance, can be taken as a point object. But if a car is travelling a distance which is not very large as compared to the size of the car, then the car can not be taken as a point object. In the figure given below, the car can not be considered as a point object as it do not cover a very long distance as compared to its own length.
It is important to note that the point object is a mathematical concept to simplify the problems.