Answer
$\approx$ $296$ $km/h$
Work Step by Step
we are given that $\frac{dx}{dt}$ = $300$ $km/h$
Law of cosines
$y^{2}$ = $x^{2}+1^{2}-2(1)(x)cos120°$
$y^{2}$ = $x^{2}+x+1$
$2y\frac{dy}{dt}$ = $2x\frac{dx}{dt}+\frac{dx}{dt}$
$\frac{dy}{dt}$ = $\frac{2x+1}{2y}\frac{dx}{dt}$
after 1 min, $x$ = $\frac{300}{60}$ = $5$ $km$
$y$ = $\sqrt {5^{2}+5+1}$ = $\sqrt {31}$ $km$
$\frac{dy}{dt}$ = $\frac{2(5)+1}{2\sqrt {31}}(300)$
$\frac{dy}{dt}$ $\approx$ $296$ $km/h$
