For the center of mass, this is not true, if anything, it's the other way around (though ideally you would know both so you could calculate DV or momentum etc etc...) Otherwise, you could have uncontrollable rotation. But for number two, where did you get that equation? M*A=F, not V F is in newtons, or kgm/s^2 speed (or velocity) is in m/s taking your original equation is Kg (mass) * m/s^2 (acceleration) = kgm/s^2 Therefore, velocity is not involved with this equation, if you wanted velocity, you would also have a time variable in there.