A steel ball of mass 8.0 kg and traveling at 3.0 m/s [E] has a head-on elastic collision with a brass ball which is at rest. After the collision, the velocity of the brass ball is 4.0 m/s [E]. Find:

Question

A steel ball of mass 8.0 kg and traveling at 3.0 m/s [E] has a head-on elastic collision with a brass ball which is at rest. After the collision, the velocity of the brass ball is 4.0 m/s [E]. Find:
a)the velocity of the steel ball after the collision
b) the mass of the brass ball
My work: I know its an elastic collision, but I have no idea how to solve for a problem that is missing mass and velocity :( any equations would be helpful!

bobpursley · Answer

start with momentum: east direction
8*3+0=Brass*4 + 8 V

so brassmass=6-4V

Now conservation of energy:
1/2 8 *9=1/2 Brassmass*16+1/2 8 *V^2

ok, but in for brassmass, 6-4V

factor it into a quadratic, and use the quadratic equation to solve for V.