posted by johnny .
The people move toward the door at speed vs = 3.7 m/s, are each d = 0.20 m in depth, and are separated by L = 1.75 m. The arrangement in the figure occuurs at time t = 0.
(a) At what average rate the layer of people at the door increase?
(b) At what time does the layer's depth reach 5.9 m? (The answer reveals how quickly such a situation becomes dangerous.)