$3-3($a$)$ If the energy loss of a $10-$Mev proton in air is $50$ kev$/$cm$,$ what is the energy loss of a $40-$Mev alpha particle? $($The answer can be written immediately.$)($b$)$ Assuming the energy$-$loss equations for protons and for nonrelativistic electrons are identical, at what kinetic energy does an electron have the same energy loss as a $10-$Mev proton?