A girl having mass mG is standing on a plank of mass mP. Both are initially at rest on a frozen lake which constitutes a frictionless and flat surface. The girl starts to walk all along the plank at a constant velocity vGP to the right relative to the plank. (The subscript GP stands for the girl relative to the plank.)
(i) Determine the velocity vPI of the plank relative to the surface of the ice? (Use the given as required: vGP, mG, and mP. Point out the direction with the sign of your answer. Let the positive direction be in the direction which the girl walks.)
(ii) Determine the girl's velocity vGI relative to the ice surface? (Use the given as required: vGP, mG, and mP. Point out the direction with the sign of your answer. Assume that the positive direction be in the direction which the girl walks.)