<PRE><B>Question 555141</B>
The stopping distance D of a car after the brakes are applied varies directly as the square of the speed R.
 If a car traveling 40mph can stop in 90ft, how many feet will it take for the same car to stop traveling 90 mph?
:
Find the constant of variation, k:
k*R^2 = D
R = 40, D = 90
k*40^2 = 90
1600k = 90
k = {{{90/1600}}}
k = .05625
:
D = .05625R^2; the equation
At 90 mph
D = .05625*90^2
D = 455.625 ft at 90 mph

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