A 75 kg person jumps from the first-floor window of a burning building and lands almost vertically on the ground with a horizontal velocity of 3 m/s and a vertical velocity of -9 m/s. Upon impact with the ground, he is brought to rest in a short time. The force experienced by his feet depends on whether he keeps his knees stiff or bends them. Find the force on his feet in each case.
You will need to find the time the impact lasts by making reasonable assumptions about the deceleration. Although the force is not constant during the impact, working with a constant average force for this problem is acceptable.
A) First, find the impulse on the person from the impact on the ground. Calculate both its magnitude (in N · s) and direction (in degrees counterclockwise from the +x-axis).
Magnitude: N · s
Direction: ° counterclockwise from the +x-axis
(b) Find the average force (in N) on the feet if the person keeps his legs stiff and straight, and his center of mass drops by only 3 cm vertically and 3 cm horizontally during the impact. (Enter the magnitude.)
N
(c) Find the average force (in N) on the feet if the person bends his legs throughout the impact so that his center of mass drops by 40 cm vertically and 4 cm horizontally during the impact. (Enter the magnitude.)
N
(d) Compare the results of part (b) and (c).
F(b)
F(c)
=
Draw conclusions about which way is better.