mass is always a constant for both kinetic and potential energy..no matter what situation any object is the mass doesnt change..velocity is always the factor that kinetic energy changes with..the lower the velocity the lower the knetic energy is ke=1/2 mv^2 they are directly related..when velocity= to zero then ke=0 however if there was no mass then that means there is no object which means kinetic energy is not present either..but usally its all about the velocity