Question

A ball strikes the floor vertically downward with a speed $5$ m/s and a rebounds with the same speed. The magnitude of its change in velocity will be?

Answer 1

Let the velocity at instance when it

strikes the ground be $v$.

Then it rebound with velocity$=(-v)$ as direction is opposite

Change in velocity$=(-v)-\left(v\right)=-2v$

$-ve$ sign implies that it is in opposite

directions of velocity we've take the magnitude.