Answer
4.78 m/s
Work Step by Step
If the frictional force is 500N we would need to find the downward force of his weight to find the net force. The downward force would be Fg = mg = 70kg * 9.8 $m/s^2$ = 686N. Therefore, the net force would be 186N downward and since F = ma, his acceleration would be 2.66 $m/s^2$.
To find his final speed, we use
$v^2 = v_{0}^2 + 2a\Delta x$ and find that v = 4.78 m/s
