Collision Q

[anonuser0511]

A proton of mass 1.0000u traveling at speed , collides with Ge nucleus of mass 71.92u; the proton rebounds in exactly opposite direction with a speed of 0.9726
A fraction of the proton's original kinetic energy is transferred to the Ge nucleus. Will that fraction be larger or smaller if a lighter nucleus is used instead of Ge? (try to do this algebraically rather than substituting numbers.)

I've been told to work out ratio of initial velocity and final velocity of the proton in terms of Ge (from conservation of momentum formula), but I'm still really confused.

[Mao]