Question

which is the body which can have zero average velocity but non-zero average speed?

Answer 1

If the displacement covered by the body is zero then the average velocity is zero. 
But the distance covered by the body can't be zero,so the average speed can't be zero .

Answer 2

First we need to understand what is average velocity and average speed.
Average velocity=Total diplacement/Total time
Average speed= Total Distance/Total time

If a body travels from Point A to Point B and then again travels From Point B back to Point A, then-
Displacement = 0
Distance = 2AB

O___________________________O
(Point-A)                                     (Point-B)

Therefore, since displacement is zero, then avg, velocity will also be zero but avg. speed would not.
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