Question 315634
I can write
{{{d = k*r^2}}}
Substituting:
{{{90 = k*40^2}}}
{{{k = 90/1600}}}
{{{k = .05625}}}
and, so
{{{d = .05625*50^2}}}
{{{d = .05625*2500}}}
{{{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)