A 30-Kg Object Moving 8

Multiple Choice

A 3.0-kg object moving 8.0 m/s in the positive x direction has a one-dimensional elastic collision with an object (mass = M) initially at rest. After the collision the object of unknown mass has a velocity of 6.0 m/s in the positive x direction. What is M?

A) 7.5 kg
B) 5.0 kg
C) 6.0 kg
D) 4.2 kg
E) 8.0 kg