A 60 kg canoeist stands at the stern of a 40 kg canoe initially at rest, then walks to the bow. By conservation of momentum the canoe must move in the opposite direction (neglecting friction with water). The center of mass does not move since the initial momentum was zero.

The expression for the conservation of momentum is , where is the momentum of the canoe and the momentum of the person walking. Substituting the values of the masses and velocities, this expression gives .