## Essential University Physics: Volume 1 (3rd Edition)

We find the velocity of each of the masses after the collision, calling v the velocity of the moving mass before the collision: $v_f = \frac{mv}{m+m}=.5v$ We compare the kinetic energies: $k_0=\frac{1}{2}mv^2$ $k_f= \frac{1}{2}(2m)(.5v)^2 = \frac{1}{4}mv^2$ Thus, we see that half of the kinetic energy was lost as a result of the collision.