Calculating Punch Force to Break Concrete Slab

[cybernerd]

Homework Statement

I am working on a physics project about karate, and I want to know how fast I would have to punch to break a practice concrete slab.

I know that the slab requires 1900 Newtons to break. I also know that my arm has an approximate mass of 8.4 kg. I also know that my arm is about 80 cm long, which is basically the distance my punch will travel.

Homework Equations

F = ma

The Attempt at a Solution

If I simply use F = ma, it tells me that I must punch at 226 m/s to break the concrete...that doesn't seem right to be. I know I'm probably oversimplifying the problem...could someone point me in the right direction?

 

[mgb_phys]

It's not just the mass of the hand/arm if there is muscle power behind it at impact
I think you might have to consider the area of the impact, the concrete has a maximum stress (force/area=pressure) that might be more important than the ulitmate load