Aboy throws a 15 kg ball at 4.7 m/s to a 65 kg girl who is stationary and standing on a skateboard. after catching the ball, the girl is travelling at: a) 0.88 m/s b) 0 m/s c) 1.1 m/s d) 3.2 m/s

Explanation:

To solve this problem we use the Momentum's conservation Law, before and after the girl catch the ball:

       (1)

At the beginning the girl is  stationary:

      (2)

If the girl catch the ball, both have the same speed:

      (3)

We replace (2) and (3) in (1):

We can now solve the equation for v_{f}:

wavelength divides in half and speed stays the same.