Gravity is one cause of acceleration. If we discount friction, e.g. air resistan

Question

Gravity is one cause of acceleration. If we discount friction, e.g. air resistance, objects falling on earth will accelerate at 32.2 feet per second change in velocity per second (ft/sec^2) or 9.81 m/sec^2. If a skydiver falls out of an airplane for 4 seconds before putting the rip cord (actually, sky divers don't use rip cords these days), how fast will that person be falling when the parachute opens. By the way, for a reference point, 60 miles pet bout is equal to 88 feet per second. Because of air resistance, a skydiver will actually accelerate to about 120 miles per hour after 11 seconds or so.

Explanation / Answer

60 miles per hour=88 feet per sec

so 120 miles per hour= 176 feet/sec

Now use the equation vf=vi+at

176=0+a*11

a=176/11= 16 feet/s^2

Now again use it for 4 sec

vf=vi+at

vf=0+16*4= 64 feet/sec

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