Posted by Jack on October 20, 2002 at 11:06:56:
In Reply to: need help with related rates~ posted by supi on October 20, 2002 at 01:35:06:
: A man starts walking north at 4 ft/s from a point P. Five minutes later a woman starts walking south at 5 ft/s from a point 500 ft due east of P. At what rate are th people moving apart 15 min after the woman starts walking?
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: Doing as T says - let s(t)=the distance between the man and woman at time t ( t in seconds). Then s(t)=sqrt[(4t+5t+1200]^2 + 500^2]
: The 1200 factor comes from the fact that the man will walk 1200 feet during the 5 min delay of the woman walking.
: At t=900 sec I get ds/dt=8.987 ft/s