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An 81 kg stuntman jumps from the top of a building 29 m above a catching net. Assuming that air resistance exerts a 100 N force on the stuntman as he falls, determine his velocity just before he hits the net

Sagot :

AL2006
In order to solve this, we can get all tangled up in acceleration,
or we can just add up the energy budget.

-- Gravitational potential energy = (mass) (grav accel) (height above something)

-- 29 m above the net, his potential energy is (81 x 9.8 x 29) = 23,020 joules

-- All the way down, air resistance exerts 100 N of force against him.
The energy burned up by air resistance is the work done = 100 x 29 = 2,900 joules.

-- The energy he has left when he hits the net is (23,020 - 2,900) = 20,120 joules.

-- When he hits the net, all of his energy is kinetic energy . . . (1/2) (m) (v²)

(1/2) (m) (v²) = 20,120

(40.5) (v²) = 20,120

v² = 20,120 / 40.5

v = square root of (20,120 / 40.5) = 22.3 meters per second (about 50 mph)
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