The forces on a dancer can be measured directly when a dancer performs a jump on a force plate that measures the force between her feet and the ground. A graph of force versus time throughout a vertical jump performed on a force plate is shown in Fig. P4.60. What is happening at 0.4 s? The dancer is

(a) Bending her legs so that her body is accelerating downward;

(b) Pushing her body up with her legs and is almost ready to leave the ground;

(c) In the air and at the top of her jump;

(d) Landing and her feet have just touched the ground.

Figure P4.60

1600 1400 1200 1000 800 600 400 200 0.5 1.0 1.5 2.0 2.5 3.0 - 200 Time (s) Force (N)