A boy goes from A to B with a velocity of 20m/min and comes back from B to A with a velocity of 30m/min. The average velocity of the boy during the whole journey is..? a) 24m/min
b) 25m/min
c) zero
d) 20m/min
with explanation please​

c) zero

Explanation:

velocity is DISPLACEMENT over TIME. If the start point and end point are identical, there is no displacement and therefore zero average velocity. This is in contrast to average Speed which is distance over time and in this case would be at least twice the distance between A and B (he may have zigged and zagged in route to increase the distance covered) over the time elapsed.

electrical to thermal