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

Algebra ->  Polynomials-and-rational-expressions -> 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      Log On


   



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) About Me  (Show Source):
You can put this solution on YOUR website!
I can write
d+=+k%2Ar%5E2
Substituting:
90+=+k%2A40%5E2
k+=+90%2F1600
k+=+.05625
and, so
d+=+.05625%2A50%5E2
d+=+.05625%2A2500
d+=+140.625
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 k that will result in feet = feet
The units for k must be (feet) / (miles/hr)