Answer
The arms exert a force of 763 N during the acceleration.
Work Step by Step
We can find the acceleration.
$y = \frac{1}{2}at^2$
$a = \frac{2y}{t^2} = \frac{(2)(0.15~m)}{(0.5~s)^2}$
$a = 1.2~m/s^2$
We can find the force $F$ exerted by the arms.
$\sum F = ma$
$F -mg = ma$
$F = ma + mg = \frac{(680~N)(1.2~m/s^2)}{9.80~m/s^2}+680~N$
$F = 763~N$
The arms exert a force of 763 N during the acceleration.