Question #6e96b

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Answer 1 · 2015-08-01T04:04:37

$v = 8sqrt(5)"m/s"$

Just after bus started
For bus: Displacement, $x = (1/2)$ x $(0.2)$ $t^2$
For man: Displacement, $80 + x = vt$

To get close to the bus:

$0.1 * t^2 = vt - 80$ ; eliminating $x$ from above two equations

=> $t^2 -10vt +800 = 0$

To get the real solution of the above quadratic equation;

$10v^2 - 4 * 1 * 80 >= 0$

This means that

$v^2 >= 320$

so, the minimum speed will be

$sqrt(v^2) = sqrt(320) => v = 8sqrt(5)"m/s"$