Solve for Velocity & Force in Jump from Roof | Physics Dynamics Help

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A person jumps from the roof of a house 4.5m high. when he strikes the ground below, he bends his knees so that his torso decelerates over an approximate distance of .7m. if the mass of his torso (excluding legs) is 45 kg, find (a) his velocity just before his feet strike the ground, and (b) the average force exerted on his torso by his legs during acceleration

...i figured out (a) v=9.4, but on b, i don't know what to do

Thanks in advance
 
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You need to find the deceleration, which you can as you know the initial and final velocities, and the distance the deceleration takes place in. You need the same equation as you used in the first part, rearrange it and solve for acceleration. Then use F=ma.
 
Since when is dynamics morbid?
 

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