0-kg girl is standing on a 151-kg plank. Both originally at rest on a frozen lake that constitutes a frictionless, flat surface.

A 44.0-kg girl is standing on a 151-kg plank. Both originally at rest on a frozen lake that constitutes a frictionless, flat surface. The girl begins to walk along the plank at a constant velocity of 1.56 m/s relative to the plank.