Elastic head-on collision physics

[Eminem04]

I need help with this problem. I tried it myself but I'm not sure if it's correct ( i got 4 m/s )
A billiard ball traveling at 4.0 m/s has an elastic head-on collision with a billiard ball of equal mass that is initially at rest. The first ball is at rest after the collision. What is the speed of the second ball after the collision?

 

[Integral]

How did you get your answer?

 

[Eminem04]

I got my answer by using M*Vi=M*Vf

 

[Kacper]

First you what to find the momentum of both cars then divide that answer by the combined mass of the two cars. But in your case since you have one car moving and one is stationary the answer is half of your moving cars velocity.

 

[HallsofIvy]

Kacper's response about "cars" confuses me!


Eminem04: Yes, your answer is completely correct. Since the two balls have the same mass and one stopped completely, the other continues forward with the same speed as the initial ball. (In a sense, it just "replaces" the first ball.)