1. In February 1955, a paratrooper fell 360 m from an airplane without being abl

Question

1. In February 1955, a paratrooper fell 360 m from an airplane without being able to open his chute but happened to land in snow, suffering only minor injuries. Assume that his speed at impact was 60 m/s (terminal speed), that his mass (including gear) was 80 kg, and that the force on him from the snow was at the survivable limit of 1.2 105 N. (a) What is the minimum depth of snow that would have stopped him safely? m (b) What is the magnitude of the impulse on him from the snow? kg·m/s

2. It is well known that bullets and other missiles fired at Superman simply bounce off his chest. Suppose that a gangster sprays Superman's chest with 5 g bullets at the rate of 105 bullets/min, the speed of each bullet being 750 m/s. Suppose too that the bullets rebound straight back with no change in speed. What is the magnitude of the average force on Superman's chest from the stream of bullets? N

Explanation / Answer

1.

Vi = initial velocity = 60 m/s

F = average force = 1.2 x 105 N

m = mass = 80 kg

a = retardation caused = F/m = 1.2 x 105 /80 = 1500 m/s2

d = stopping distance

Vf = 0 m/s

Using the equation

Vf2 = Vi2 + 2 a d

02 = 602 + (2) (-1500) d

d = 1.2 m

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