Consider the following scenario:
I am alone in space with a ball. I threw the ball at a certain speed such that i am propelled backwards (like a rocket is) as to conserve momentum. Now, since my momentum changed, so does my kinetic energy. By Work-Kinetic Energy Theorem, if there is a change in kinetic energy, there should also be work that caused it. Who did work on me?
What about the force? My body’s center of mass can not accelerate if there is no external force (Newton’s second law). What applied force on my body (if there’s any)?
I am just not a fan of “conservation of such and such says so”. I just want some cause to the change of my velocity since this is still in the realm of newtonian dynamics’ validity.