How is Kinetic Energy Conserved in an Elastic Collision?

[fizziksr0cks]

Homework Statement

A 8.5 kg steel ball, traveling left to right at 12 m/s, undergoes an elastic collision with a 5 kg steel ball at rest. To the nearest Joule, what is the Total Kinetic Energy of the two balls after collision? If the first ball has a mass of 10 kg and the second ball is traveling at it with a speed of 3 m/s, what is the velocity, to one decimal place, of the first ball after collision? What is the velocity of the second ball to one decimal place?

Homework Equations

1/2mv_i²+1/2mv_ii²=KE

The Attempt at a Solution

Question 1:
1/2 (8.5)(12²)= 612 J
Question 2 & 3:
I'm not sure the equation needed to solve for the needed. I'm pretty sure that if I can get question 2 then the same method will be used to solve question 3.

 

[kuruman]

For questions 2 and 3 you need to conserve momentum in addition to energy conservation.