(а) (b) Fnet (N) 500- 400 - Dancer begins 300 |bending knees./ 200- Dancer leaves ground. 100 - 0- t (s) 0.10 0.30 / 0.50 0.70 - 100 - -200 -300 FIGURE P9.84 -400 -
Understanding the details of timing and forces in motion can improve the performance of athletes, including dancers. Consider the forces involved in a ballet jump called a sauté demi plié. P9.84a shows the sequence of moves in the jump. The dancer starts upright, then quickly bends her knees, moving downward. After she reaches the bottom of this dip, she extends her legs, pushing herself upward. After this upward push, she leaves the ground, beginning a short period of time in the air. P9.84b is a slightly idealized graph of the net force on a 42 kg dancer executing this move.
At what time does the dancer reach the lowest point of her motion, when her speed is zero?
A. 0.20 s
B. 0.40 s
C. Between 0.40 s and 0.70 s
D. After 0.70 s
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