SOLUTION: Please help! 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 60 mph can stop in 200 ft, how many fe

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Question 433080: Please help!
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 60 mph can stop in 200 ft, how many feet will it take the same car to stop when it's traveling 70 mph?
Found 3 solutions by stanbon, josmiceli, Alan3354:
Answer by stanbon(75887)   (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 60 mph can stop in 200 ft, how many feet will it take the same car to stop when it's traveling 70 mph?
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d = k(r^2)
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Solve for "k" using "a car traveling 60 mph can stop in 200 ft".
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200 = k(60)^2
k = 200/3600 = 1/18
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Equation:
d = (1/18)r^2
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How many feet will it take the same car to stop when it's traveling 70 mph?
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d = (1/18)(70^2)
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d = (1/18)4900
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distance = 272.22 ft
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Cheers,
Stan H.

Answer by josmiceli(19441)   (Show Source):
You can put this solution on YOUR website!
The formula for this takes the form
where is the
so-called "constant of proportionality"
You have to find , so

Now, if the car travels mi/hr,

ft

Answer by Alan3354(69443)   (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 60 mph can stop in 200 ft, how many feet will it take the same car to stop when it's traveling 70 mph?
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The distance is a function of the square of the speed.
The speed increases by a ratio of 7/6, so the distance increases by (7/6)^2
200*(7/6)^2 = 272.222... feet