Question

MEDAL GIVEN TO CORRECT ANSWER.
April sits at rest on a skateboard. She has a mass of 65 kg. Her friend throws her a suitcase (m = 15 kg) at a speed of 3 m/s. If she catches it, how fast will she, the skateboard, and the suitcase move?

A. 3.0 m/s
B. 0.56 m/s
C. 1.1 m/s
D. 0.69 m/s

Answer 1

First we must find the total initial momentum

Remember, momentum is mass times velocity.
April is initially not moving, so her initial momentum is 0.
The suitcase IS moving, so its initial momentum is (15kg)(3m/s) = 45 kgm/s

So the total INITIAL momentum is 0 + 45 = 45 kgm/s.


Now remember, according to conservation of momentum, the initial momentum must equal the final momentum.

So...

45 kgm/s = (65kg + 15kg)V <----- Here we add the mass of the girl AND the suitcase
45kgm/s = (80kg)V <--------- Must solve for V
V = .56

Answer 2

So the correct answer is B