Question

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. After buying a book, he travels the same distance in the same time to reach back in the classroom. Find (a) average speed, and (b) average velocity, of the boy.

Answer 1

(a) Distance travelled is the length of the actual path covered.
Total distance covered in going and coming back:
= (20 + 20) m
= 40 m
Total time taken, = (25 + 25) s
= 50 s
So, we can calculate average speed as:
$\mathrm{Average}\mathrm{speed}=\frac{\mathrm{Total}\mathrm{distance}\mathrm{travelled}}{\mathrm{Time}}$
Average speed for the entire journey:
$$\begin{gathered} =\frac{40}{50} \\ =\boxed{0.8\mathrm{m}/\mathrm{s}} \end{gathered}$$

(b) Average velocity is zero, as displacement is zero because the boy arrives at the initial point.