Question 320142
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 70 mph can stop in 270 ft, how many feet will it take the
 same car to stop when it is traveling 30 mph.
:
Use a ratio equation, find d for 30 mph:
{{{70^2/30^2}}} = {{{270/d}}}
:
{{{4900/900}}} = {{{270/d}}}
cross multiply
4900d = 900 * 270
:
4900d = 243000
d = {{{243000/4900}}}
d = 49.6 ft, stopping distance at 30 mph