Kinetic Energy Dissipation in a Colliding System

[tater08]

Homework Statement

A hockey puck B rests on a smooth surface of ice and is struck by a second puck A , which was originally traveling at 40.0 m/s and which is deflected 30.0 degrees from its original direction. Puck B acquires a velocity at a 45.0 degree angle to the original direction of A . The pucks have the same mass.

what fraction of the orignal kinetic energy of puck A dissipates during the collision.

Homework Equations

(Delta K) /K
KE=0.5 mv^2

The Attempt at a Solution

i was able to solve for the velocity of both block a and b. But now i can't seem to figure out the original kinetic energy. I do not know where to go with the masses being the same.
Va=29.3 m/s
Vb=20.7

 

[Redbelly98]

You can express the kinetic energy in terms of the unknown mass "m", and go from there.

 

[tater08]

(Kei-Kef)/ KEi = ((1-(m1/m1+m)) KEi)/KEI = M2/m1+M2 1/ (1+1) KE should be 0.5 or 50 percent. But this is the wrong answer And I'm Totally lost. thanks for any help that i may receive.

 

[tater08]

I figured it out. 1-(KEf-KEi)/KEI is basically the equation to use.