Question

Object A with a mass of 1.5 kilograms is moving with a velocity of +11.2 meters/second (moving in the +x direction). It has a perfectly elastic collision with stationary object B that has a mass of 4.5 kilograms. After the collision, object B travels with a velocity of +5.6 meters/second. What is the final velocity for object A?
A. +3.8 meters/second in the same direction
B. -3.8 meters/second in the opposite direction
C. +5.6 meters/second in the same direction
D. -5.6 meters/second in the opposite direction
E. -6.2 meters/second in the opposite direction

Answer 1

Conservation of momentum:

Before = After

m1 v1 +m2 v2 = m1 v1' + m2 v2'

If needed you could also use conservation of energy, here all kinetic, since the collision is elastic, meaning no energy loss.