Question

A boy 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

Answer 1

`a)v_(f)=0.88m/s`

Step-by-step explanation:

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

`\\ p_(1)=p_(2)\\m_(ball)*v_(o.ball)+m_(girl)*v_(o.girl) = m_(ball)*v_(f.ball) + m_(girl)*v_(f.girl)` (1)

At the beginning the girl is stationary:

`v_(o.girl)=0m/s` (2)

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

`v_(f.girl)=v_(f.ball)=v_(f)` (3)

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

`m_(ball)*v_(o.ball) = (m_(ball)+m_(girl))*v_(f) \\`

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

`v_(f)=(m_(ball)*v_(o.ball))/((m_(ball)+m_(girl)))=(15*4.7)/(15+65)=0.88m/s`