stopping distance

Question

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
30 mph can stop in
40 ?ft, how many feet will it take the same car to stop when it is traveling 120 mph?

Answer 1

d=Ar^2 where A is the coefficient of proportionality. 

 

With the given information, we have enough to solve for "A"

 

40=A*(30)^2,

 

A=40/900 which is approximately 0.44.

 

Now the equation reads,

 

d=0.044r^2, plugging in 120 for r and solving for d gives.

 

d=633.6 ft