Answer:
15 m/s
Step-by-step explanation:
m₁ = 9 kg, before collision: v₁ = 5 m/s, after collision: v₁' = 0
m₂ = 3 kg, before collision: v₂ = 0, after collision: v₂' = ? (x)
Momentum conservation:
9 * 5 + 3 * 0 = 9 * 0 + 3 * x
45 = 3x
x = 45/3 = 15 m/s