# Smart pedestrian

Classical Mechanics Level 4

A truck of width $$l$$ is moving with a uniform speed $${v}_{0}$$ along a straight horizontal road. A pedestrian starts to cross the road with a uniform speed $$u$$ when the truck is $$d$$ away from him. The minimum value of $$u$$ so that he can cross the road safely is of the form $$\frac{m}{\sqrt{n}}$$ where $$m$$ and $$n$$ are coprime and $$n$$ is square free. Find $$m-n$$.
Details
$$l=2m\\{v}_{0}=8m{s}^{-1}\\d=4m$$

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