A skydiver with mass $85\mathrm{.}0$ kg drops out of a hovering helicopter and falls $700\mathrm{.}0$ m before pulling the ripcord and releasing his parachute. $($a$)$ Find the work done by gravity. $($b$)$ What would be the speed just before opening the chute if there was no air resistance? $($c$)$ If the actual speed just before the chute opens is $50\mathrm{.}0$ m$/$s$,$ what was the average force of air resistance? $($d$)$ Once the parachute is open, the air does work in amount $175,000$J as the speed is decreased to $6\mathrm{.}00$ m$/$s$.$ What distance does the skydiver fall while this happens?