A 42.5 kg student runs down the sidewalk and

Question

jumps with a horizontal speed of 4.16 m/s
onto a stationary skateboard. The student
and skateboard move down the sidewalk with
a speed of 3.97 m/s.
a) Find the mass of the skateboard.

Answer 1

Now Angel, this is very similar to the one I answered for you.
Momentum after = momentum before.