A child of mass m runs on ice with velocity v(o) and steps on the

end of a plank of length l and mass M that is perpendicular to the

child’s path, as shown.


(a) Describe quantitatively the motion of the system after the

child is on the plank. Neglect friction with the ice.


(b) One point on the plank is at rest immediately after the collision. Where is it?