A 48.9 kg girl is standing on a 129 kg plank. The plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless surface. The girl begins to walk along the plank at a constant velocity of 1.20 m/s relative to the ice surface in the direction of the positive x-axis.
What is the velocity of the plank relative to the ice surface?
(in m/s)
What is the velocity of the girl relative to the plank?
(in m/s)