Answer:
6.4 m/s
Step-by-step explanation:
This is a conservation of momentum problem. Total momentum (P = mv) before the collision must equal the total momentum after the collision.
(4 kg)(8 m/s) + (2 kg)(0 m/s) = (4 kg)(4.8 m/s) + (2 kg)v
Before = After
Solve for v, the velocity of the 2 kg ball after the collision:
32 kg·m/s + 0 = 19.2 kg·m/s + (2 kg)v
12.8 kg·m/s = (2 kg)v
v = (12.8 kg·m/s) / (2 kg) = 6.4 m/s
This makes sense because after the collision the 4 kg ball slows down and the 2 kg ball speeds up (from rest)