physics help!!! momentum!?

Question

momentum

QUESTION: Consider a system of two balls. Ball "A" has a mass of 9.2 kg and ball "B" has a mass of 7.5 kg. Ball "A" is going +15 m/s when it strikes ball "B" which is at rest. After the collision what is ball "Bs" velocity if ball " A" is moving with a velocity of 3.8 m/s

ANSWER: 14 m/s
( i know the answer because the teacher told us but i dont know how to do it, thanks for the help!)

Show procedures if you know how to do it please. thanks soo much!

Answer 1

First, remember that mass* velocity = Momentum. Ball A has mass 9.2 and has velocity 15 m/s, so we mulitply those two to get the answer:
(9.2kg)(15m/s)=138 kg*m/s
So, A has a momentum of 138 kg*m/s. then, we need to find its momentum after it hit B, so we do the same equation with the new velocity:
(9.2kg)(3.8m/s)=34.96kg*m/s
Then, we subtract the final momentum from the initial momentum
138-34.96=103.04
then, we put that number as the momentum of Ball B afrter collision, then put in Ball B's mass, and then solve for v
103.04=(7.5 kg)(v)
103.04kg*m/s /7.5kg=v
13.7=v (the answer would then be rounded up to 14, I guess.
Hope this helps!

Answer 2

Linear momentum is always conserved. The total momentum is

(9.2 kg)(+15 m/s) + (7.5)(0) before the collision
(9.2 kg)(+3.8) + (7.5)(v) after the collision

Set these two expressions equal to each other and solve for the unknown velocity v. I get a bit less than 14 m/s.

Answer 3

I had physics last year and was so good at this kind of stuff but now I can't remember how to do it, sorry.