Question

A boy walks from his classroom to the bookshop along a straight corridor towards North. He covers a distance of 20 m is 25 seconds to reach the bookshop. After buying a book, he travels the same distance at the same time to reach back in the classroom. Find (a) average speed, and (b) average velocity, of the boy.

Answer 1

A boy walks from his classroom to the bookshop along a straight corridor towards North. He covers a distance of 20 m in 25 seconds to reach the bookshop
Distance from classroom to bookshop = 20m
Time = 25sec
After buying a book, he travels the same distance at the same time to reach back into the classroom.
(a) Average speed = $\frac{TotalDistance}{TotalTime}$ = $\frac{20+20}{25+25}$ = $\frac{40}{50}$ = 0.8 m/s
(b) Average velocity= $\frac{Displacement}{Time}$
As displacement is the shortest path between source and destination.
Here, displacement = 0, because child travels 20m forward and travels 20 m backward.
Displacement = 20 - 20 = 0
Hence, average velocity = $\frac{0}{50}$ = 0 m/s