First, we start with
- Let m = mass of the fist and arm of a 45 kg (100 pound) martial artist, approximately 10 kg (22 pounds).
- Let K = kinetic energy solved in lesson 1,
Next, plug and chug:
This shows that the initial assumption of 5 m/s was close enough. We can re-visit lesson 1 and show the difference in energy and force.
Insert corrected values:
Note that with a 1.1 m/s change in velocity, there is about a 50J change in energy delivered, but the force applied does not change! Force is a product of mass and acceleration, not velocity! To state that again, as long as I set my initial conditions such that the initial guess on velocity is close, I can back-derive the actual velocity by focusing on the key variables of mass and acceleration. The work shown above has been abbreviated. I leave the full derivation up to the martial arts physicist who happens upon this lonely blog.