Abel flicks a 20g marble at a speed of 0.5 m/s. It has one dimensional collision with a 10g bouncy ball, that was initially at rest. After they collide, the bouncy balls speed is 0.5 m/s. What is the marbles post-collision speed? Show whether or not any kinetic energy lost during the collision.

Linear momentum must be conserved. Use that fact to compute the marble's post-collision speed, v.

20*0.5 = 10*0.5 + v*20
5 g*m/s = 20 v
v = 0.25 m/s (forward)

Initial KE = (1/2)*0.020*0.5^2 = 2.5*10^-3 J
Final KE = (1/2)*0.020*(0.25)^2 + (1/2)* 0.010*(0.5)^2 = 1.875*10^-3 J
(masses had to be entered in kg to get answers in Joules)