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

 

[nlightner]

I would suggest taking into consideration the material properties of the concrete slab. Concrete is a composite material made up of cement, water, and aggregates such as sand and gravel. The strength of concrete can vary greatly depending on the mix and curing process. Additionally, the thickness and dimensions of the slab can also affect its strength.

To accurately calculate the punch force needed to break the slab, you will need to consider the compressive strength of the concrete, which is typically measured in megapascals (MPa). This value represents the maximum amount of force per unit area that the concrete can withstand before it fails.

You can then use the formula F = P x A, where F is the force, P is the pressure (in MPa), and A is the cross-sectional area of the slab that will be impacted by your punch. This will give you the minimum force needed to break the slab.

However, it is important to note that the force required to break the slab will also depend on the speed and technique of your punch. If you punch at a slower speed, you may need a higher force to break the slab. Additionally, the angle and location of impact can also affect the force needed.

In conclusion, while F = ma can provide a general estimate, it is important to consider the specific properties of the concrete slab and the mechanics of your punch in order to accurately calculate the punch force needed to break the slab.