Question

According to a newspaper account, a paratrooper survived a training jump from 1200 ft when his parachute failed to open but provided some air resistance by ï¬apping unopen in the wind. allegedly he hit the ground at 100 mi/h after falling 8 seconds. test the accuracy of this account.

Answer 1

Let's make a few assumptions. 1. The paratrooper's lowest speed will be just prior to impact. 2. Since the jump was from a relatively low altitude, the paratrooper used a static line and the parachute should have opened almost immediately upon jumping. So let's convert 100 mi/h to ft/s 100 mi/h * 5280 ft/mi / 3600 s/h = 146.67 ft/sec Given the 1st assumption above, the MAXIMUM distance the paratrooper would have fallen would be 8 seconds at 146.67 ft/s, so 8 s * 146.67 ft/s = 1173.36 ft The calculated distance is close to the jump distance, which agrees with both assumptions 1 and 2. So this account does seem reasonable. Additionally, looking for the speed of a parachutist doing a freefall in the belly-to-earth position with arms and legs outspread, they will generally reach a terminal velocity of 120 mi/h which is slightly faster than the 100 mi/h in the article. This too is in agreement with the defective parachute flapping and causing some extra air resistance.