The answer would be
A 50-g ball moving at 10 m/s in the +x direction suddenly collides head-on with a stationary ball of mass 100 g. If the collision is perfectly elastic, what is the velocity of each ball immediately after the collision?
A) -3.3 m/s, +6.7 m/s
B) +3.3 m/s, -6.7 m/s
C) -6.7 m/s, +3.3 m/s
D) +6.7 m/s, -3.3 m/s
The answer would be A.