Answer
a) 27.9 mi/h
b) 166.7 ft.
Work Step by Step
a) Substitute 0.4 for $f$, and 65 ft for $d$. Using the equation $s = \sqrt {30fd}$, we can find that s = 27.9 mi/h.
$s = \sqrt {30\times 0.4 \times 65}$
$s = \sqrt {780}$
$s = 27.9$
b) Substitute 0.5 for $f$, and 50 mi/h for $s$. Using the equation $s = \sqrt {30fd}$, we can find that d = 166.7 ft.
$50 = \sqrt {30\times 0.5d}$
$2500 = 15d$
$d = 166.7$
