Answer
Speed of the car $=67 \;mph$.
Work Step by Step
The formula for the speed is
$s=\sqrt{30fd}$
The given values are
Length of the skid marks $d=150\; feet$.
Coefficient of friction $f=1$.
Substitute all values into the formula.
$\Rightarrow s=\sqrt{30(1)(150)}$
Simplify.
$\Rightarrow s=\sqrt{4500}$
Use calculator.
$\Rightarrow s=67.082039325$
Approximate value.
$\Rightarrow s=67\;mph$.
