Question

a cyclist is riding on a circular path of radius 5 m with speed of 1 m/s.what is the change in velocity when he has travelled through a semicircle (with calculations)

Answer 1

Here the guy is moving with 1 m/s speed in one direction and return in another direction so his avg velocity would be
1-(-1)/t. ( as velocity is vector)

also
$t = \frac{distance}{speed}$
$t = \frac{\pi \times 5}{1}$
Therfore

$avg \: velocity = \frac{2}{5\pi}$

Answer 2

change in velocity =final v - initial v
= (+1) -(-1)
=1+1
=2m/s