Answer
The correct answer is (a) bending her legs so that her body is accelerating downward.
Work Step by Step
Initially, the dancer is standing on the force plate. The normal force is just above 600 N, which is equal in magnitude to the dancer's weight. As the dancer bends her legs, her center of mass accelerates downward, and this reduces the normal force, as we can see in the graph. At t = 0.5 seconds, the dancer starts to push up off the ground, and the normal force starts to increase, as we can see in the graph.
At t = 0.4 seconds, the normal force is decreasing because the dancer is bending her legs so that her body is accelerating downward. The correct answer is (a).
