SOLUTION: 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 fo

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Question 555141: 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?
It will take ______ft.
Please help with this word problem. Thank you.

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
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%2F1600
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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