Askydiver weighing 180lbs (including equipment) falls vertically downward from an altitude of 5000 ft and opens the parachute after 10 s of free fall. assume that the force of air resistance, which is directed opposite to the velocity, is of magnitude.75|v| when the parachute is closed and is of magnitude 12|v| when the parachute is open, where velocity v is measured in ft/s. find the speed of the skydiver when the parachute opens.