# physics

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A person falls from a height of 2.0m on earth(a=g=9.8m/s2). What acceleration is necessary for them to stop over 30 cm (assuming they bend their knees)? what if they don't bend their knees hence stop over a distance of 1 mm?

• physics -

First calculate the person's velocity when the feet hit the ground.
V = sqrt(2gH) To decelerate to zero velocity while the center of mass moves a distance X requires a deceleration rate (a) that is given by the formula

V = sqrt(2aX)

The two equations can be combined to give:

a = V^2/2X = 2gH/2X = g*H/X

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