ive got this problem in which i am given: the work function of tungsten = 4.5 eV light with photon energy 5.8 eV illuminates surface and i need to figure out what the velocity of the fastest electron ejected from the surface is. so i see work function and 'fastest' and i think, ok KEmax = hf - work function. and KE is just .5mv^2. the problems i run into are these: where do i get f? or hf? i see that E = hf , so i think, ok i will use 5.8 -4.5 = KEmax. but then i run into another problem. which mass do i use? i got really screwed up with the units... i can use 9.109e-31 kg but i dont know if and eV is kg m^2/s^2. i am also given the mass of an electron as .511 MeV/c^2 but i dont really understand what that means. is it .511e6 or .511e6/(3e8)^2?? if you have any insightful comments, i would be very grateful.