Answer
(a) $2.64s$
(b) Please see the work below.
Work Step by Step
(a) We can find the required time as follows:
$t=\sqrt{\frac{2\Delta y}{T/m-g}}$
We plug in the known values to obtain:
$t=\sqrt{\frac{2(3.40)}{(755)(70)-(9.81)}}$
$t=2.64s$
(b) We know that if Jones is pulled out in less time than that calculated in part (a) then the acceleration will be increased and as a result the tension in the rope will exceed $755N$ and the rope will break.
