physics
posted by risha .
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?

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