4. A steel cube (m = 50.0 g) is launched horizontally with a velocity of 40.0 m/s
toward a ball of silly putty (m = 0.500 kg) at rest on a frictionless surface. They
collide completely inelastically, then undergo a second collision with a larger
steel cube (m = 200.0 g). The second collision is elastic. What is the final
velocity of the larger steel cube?
