I have noticed just in the past couple of years that I get a red splotchy rash on my neck when I drink beer. I thought it might be an allergic reaction, but it doesn't happen all of the time when I drink beer. I have tried switching to a different kind of beer, but I still have random outbreaks of this rash. Answer.
So, if two objects have the same energy $E_k$, they only have the same momentum if they also have the same mass. Since the bull has a much larger mass than the bullet, it must therefore have a much larger momentum than the bullet to arrive at the same kinetic energy. Force is change of momentum with time, $F = \dot p$.
Thus. When the particle is at rest, its relativistic mass has a minimum value called the rest mass m rest. The rest mass is always the same for the same type of particle. For example, all protons have identical rest masses, and so do all electrons, and so do all neutrons; these masses can be looked up in a table. As the particle is accelerated to ever higher speeds, its relativistic mass increases without limit.