When a person parachutes, the impact velocity is equal to that attained in free fall from a height of 4.5 m. After contacting the ground, the jumper's momentum is quickly brought to zero by the Earth. What is: a. the impact velocity b. the impulse of the ground on the jumper, assuming a mass of 80 kg c. the average force on the jumper's feet if (i) he lands stiff-legged and the impulse only last 0.019 s and (ii) he lands with his knees flexed, so that the impulse is extended over a time interval of 0.050 s

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