The boy jumps from the boat to the shore while the boat begins to move in the opposite direction

The boy jumps from the boat to the shore while the boat begins to move in the opposite direction, which law of physics allows to explain this phenomenon.

The boy and the boat are closed systems (the resultant of external forces is zero), the impulse (product of mass and speed) from the boy is transmitted to the boat, which moves in the opposite direction (Newton’s third law) at a speed that depends on the boy’s speed at the time of the jump, his mass, as well as the mass of the boat itself.