A 2 kg clay ball traveling left to right at a speed of 6 m/s strikes and sticks to a 10 kg ball at rest. What is the fractional loss of kinetic energy after collision?
For the final velocity V of both, use conservation of momentum.
2*6 = 12*V
V = 1 m/s
KE went from (1/2)*2*6^2 = 36 J to (1/2)*12*1^2 = 6 J
5/6 of the KE is lost.