Physics of man breaking arm falling into pool

[hexum]

Homework Statement

I am figuring out the physics of the scene in the movie Get Him to the Greek where an actor falls into a pool but breaks his arm by hitting it on the concrete edge.

Mass of actor = 73 kg
Mass of arm = 4.75 kg

Force to break an arm = 73 N

Duration of fall = 3.0 s

Homework Equations

average impact force = m* V/dT

height of fall = 1/2*9.8*3.0² = 44.1 m

The Attempt at a Solution

F = m V/dT = m sqrt(2gH)/dT = 4.75*sqrt(2*9.8*(44.1))/1 = 214.6

Because 214.6 N is obviously greater than 73 N, which is the force to break an arm, then the physics in this situation seem to be good. However, I am confused on how to calculate dT. As you can see, it is 1 in the equation, but I do not see why it is not 3, which is the total time of the fall. I am told that this is the "impact interval." How exactly am I suppose to calculate this?

 

[rock.freak667]

I believe that 1 is an initial assumption since I don't think you can get the actual impact time. But you can see that the impact time would be less than 1 second. So the impact force at dT<1 would be greater than the force at dT = 1.