Question

Two billiard balls move toward each other on a table. The mass of the number three ball, m1, is 5 g with a velocity of 3 m/s. The mass of the eight ball, m2, is 6 g with a velocity of 1 m/s. After the balls collide, they bounce off each other. The number three ball moves off with a velocity of 5 m/s. What is the final velocity and direction of the eight ball?

Answer 1

This question deals with the law of conservation of momentum, which basically says that the total momentum in a system must stay the same, provided there are no outside forces. Since you were given the mass and velocity of the two objects you can find the momentum (p=mv) of each and then add them together to find the total momentum of the system before they collide. This total momentum must be the same after they collide.  Since you have the mass and velocity of one of the objects after the collision you can find the its momentum after.  Subtract this from the the system total and you will have the momentum of the other object after the collision.  Now that you know the momentum of the other object you can find its velocity using p=mv and its mass from before.

Be careful with the velocities.  They are vectors, so direction matters.  Typically moving to the right is positive (+) and moving to the left is negative (-).  It is not clear from your question which direction the objects are moving before and after the collision.

Answer 2

Answer: +5.7 m/s

Explanation: I had the same question for physics.