To solve this problem we will apply the concept related to the conservation of the Momentum. We will then start considering that the amount of initial momentum must be equal to the amount of final momentum. Considering that all the objects at the initial moment have the same initial velocity (Zero, since they start from rest) the final moment will be equivalent to the multiplication of the mass of each object by the velocity of each object, so
Initial Momentum = Final Momentum
Here,
= mass of Raft
= Mass of swimmers 1
= Mass of swimmers 2
= Initial velocity (of the three objects)
= Velocity of Raft
Replacing,
Solving for
Therefore the velocity the rarft start to move is 0.3618m/s