In order to work out this question, we must know the momentum of the marbles.
Marble 1 momentum:
Momentum1 = mass * velocity
Momentum1 = 5 * 5
Momentum1 = 25g cm/s.
Marble 2 momentum:
Momentum2 = mass * velocity
Momentum2 = 5 * 0
Momentum2 = 0g cm/s
Therefore, the total momentum of the marbles is equal to 25g cm/s.
Momentum is ALWAYS conserved in a collision! Meaning, the momentum before and after the marbles hit must be equal. Since marble 1 comes to a complete rest and there is no mention of a change in mass, Marble 2’s velocity must equal 5m/s due to conservation of momentum!
:)