Question

When you jump from an elevated position you usually bend your knees upon reaching the ground. By doing this, you make the time of the impact about 10 times as great as for a stiff-legged landing. In this way the average force your body experiences is
A) less than 1/10 as great.
B) more than 1/10 as great.
C) about 1/10 as great.
D) about 10 times as great.

Answer 1

Answer:

C) about 1/10 as great.

Explanation:

We use the relation between Impulse, I, and momentum, p:

$I=\Delta p\\ F*t=m(v_{f}-v{o})$

$F=m(v_{f}-v{o})/t=-mv{o}/t$     the final speed is zero

We can see that the average Force is inversely proportional to the time, so if the time is 10 times bigger, the average Force is 1/10 as great

Answer 2

Average force body experience is about 1/10 as great as  when the legs are kept stiff

Impact force

from Newtons second law, force. f is the product of mass, m and acceleration, a

f = m * a

a = ( v - u ) / t

f = m * ( v- u ) / t

so force is inverrsely related to time, making the time of the impact 10 times as great as stiff-legged landing impiles mathematically as follows:

for stiff-legged

f1 = m * ( v - u ) / t

for bent knees

f2 = m * ( v - u ) / 10t

f2 = f1 / 10

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