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 90 ft, how many feet will it take t

Question 315634: 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 90 ft, how many feet will it take the same car to stop when it is traveling 50mph
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
I can write

Substituting:

and, so

The car will stop in 140.625 ft
Notice that I've got feet on the left side of the equation
and miles per hour on the right side. That means I have
to pick units for that will result in feet = feet
The units for must be (feet) / (miles/hr)
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