Homework Help: Calculating the force of a kick

1. Nov 2, 2012

Oral B

1. The problem statement, all variables and given/known data
I'm writing a paper about wearing jockstraps in sports, and I'm trying to calculate whether the force of an average kick could rupture a testicle (Yeah, it hurts just to even think about). I would like to get the end result in lbs, so I'm using the metric system in the equation and then converting newtons to lbs. I would just like to confirm that I'm calculating this correctly. As a side note, can this be called psi as well? Like if the end result is 77lbs, would that also mean 77 psi?

Variables:
Average kick speed: 30 m/s (I'm aware that this is the velocity of a kick, but I'm guessing that the average kick will not exceed 30 m/s coming from rest).
Average mass of a leg: 11.5 kgs.
Testicular rupture occurs at ~110lbs of force

2. Relevant equations
F = MA

3. The attempt at a solution

F = (30)(11.5)
F = 345 Newtons, or ~77lbs.

Last edited: Nov 2, 2012
2. Nov 2, 2012

3. Nov 2, 2012

... Why?

4. Nov 2, 2012

HallsofIvy

I don't know that I would say "troll" but the problem you give simply is not solvable. You could use the information you have to find the kinetic energy in the kick and then set "force times distance" equal to that energy but you have two unknowns. You would also need to calculate the distance the foot moves from the time of impact to stopping. That would require information such as the resistance to the kick.

5. Nov 2, 2012

Oral B

Ah alright that makes sense, thank you. I will probably just settle with finding the kinetic energy and go from there, thanks for your help.

6. Nov 2, 2012

PhanthomJay

As a side note, pounds and psi are not the same. A pound is a force unit and psi is shorthand for pounds per square inch, which is a pressure or stess unit. 77 pounds acting on 1 sq in is 77 psi pressure; 77 pounds acting on 2 sq in is 38.5 psi, etc.