Inelastic collision of an electron and a mercury atom

[dswatson]

An electron with a kinetic energy of 4.9eV collides inelastically with a stationary mercury atom. Why can you assume almost 100% of the electron's energy can go into raising the mercury atom to its first excited state?

I know that with an inelastic collision both energy and momentum are conserved but I'm just not sure how to word it or show that it is true.

M(electron)=5.49E-4 u
u = atomic mass unit
M(Hg)=201u

thank you in advance

 

[nasu]

It's like the inelastic collision between a ball of mud and a wall. The kinetic energy is almost completely lost and converted into internal energy.
It happens when the mass of the second object is much larger than the mass of the first one. (atom versus electron).