CBSE Class 9 Answered

1. Displacement of a body is the change in its position.It is the shortest distance between the initial and final position of the body. So when the initial and final position of the body is same the displacement would be zero.

eg: If you are travelling along a circular track of radius r ,starting from a point A and you reach back at the same point A in some time.The distance travelled will be equal to 2πr (equal to the circumference of the track) . Since the initial and final position are the same the displacement = zero

2. Average velocity of a body = Total displacement / total time taken

Average speed of a body = Total distance / total time taken

When the body moves in a single straight line in a particular direction , the magnitude of average velocity equal to average speed as the magnitude of displacement of the body is equal to the distance travelled by the body.