Question

A 70-kg woman jumps from the first-floor window of a burning building and lands almost vertically on the ground with a horizontal velocity of 5 m/s and vertical velocity of -8 m/s. Upon impact with the ground she is brought to rest in a short time. The force experienced by his feet depends on whether she keeps her knees stiff or bends them. Find the force on her feet in each case. a. First find the impulse on the person from the impact on the ground. Calculate both its magnitude and direction. b. Find the average force on the feet if the person keeps her leg stiff and straight and her center of mass drops by only 1 cm vertically and 1cm horizontally during the impact. c. Find the average force on the feet if the person bends her legs throughout the impact so that her center of mass drops by 40cm vertically 4cm horizontally during the impact. d. Compare the results of b and c and draw conclusions about which way is better. You will need to find time the impact lasts by making reasonable assumptions about the deceleration. Although the force is not constant during the impact, working with constant average force for this problem is acceptable.

          A 70-kg woman jumps from the first-floor window of a burning building and lands almost vertically on the ground with a horizontal velocity of 5 m/s and vertical velocity of -8 m/s. Upon impact with the ground she is brought to rest in a short time. The force experienced by his feet depends on whether she keeps her knees stiff or bends them. Find the force on her feet in each case.
a. First find the impulse on the person from the impact on the ground. Calculate both its magnitude and direction.
b. Find the average force on the feet if the person keeps her leg stiff and straight and her center of mass drops by only 1 cm vertically and 1cm horizontally during the impact.
c. Find the average force on the feet if the person bends her legs throughout the impact so that her center of mass drops by 40cm vertically 4cm horizontally during the impact.
d. Compare the results of b and c and draw conclusions about which way is better.
You will need to find time the impact lasts by making reasonable assumptions about the deceleration. Although the force is not constant during the impact, working with constant average force for this problem is acceptable.

A 70-kg woman jumps from the first-floor window of a burning building and lands almost vertically on the ground with a horizontal velocity of 5 m/s and vertical velocity of -8 m/s. Upon impact with the ground she is brought to rest in a short time. The force experienced by his feet depends on whether she keeps her knees stiff or bends them. Find the force on her feet in each case.
a. First find the impulse on the person from the impact on the ground. Calculate both its magnitude and direction.
b. Find the average force on the feet if the person keeps her leg stiff and straight and her center of mass drops by only 1 cm vertically and 1cm horizontally during the impact.
c. Find the average force on the feet if the person bends her legs throughout the impact so that her center of mass drops by 40cm vertically 4cm horizontally during the impact.
d. Compare the results of b and c and draw conclusions about which way is better.
You will need to find time the impact lasts by making reasonable assumptions about the deceleration. Although the force is not constant during the impact, working with constant average force for this problem is acceptable.

Added by Nicole P.

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