Question

A 20-kg boy runs at 4 m/s  and jumps on a rest 5-kg skateboard. (1) Find the skating velocity. (2) Which law do you apply to solve this problem?   

Answer 1

`3.2 ms^-1`

Explanation:

Applying the law of conservation of momentum,assuming that their will be no other external forces acting on the collision,i.e the boy jumping on the skate board.

Let,the boy with the skate board move with velocity `v` after the jump,

So,final momentum becomes `(20+5)×v Kgms^-1`

And initial momentum was `20×4 + 5×0=80 Kgms^-1`

So,applying law of conservation of momentum,we get,

`80=25v`

So, `v=3.2 ms^-1`