nemoćan

1. feeble; infirm; frail
   Deda je već star i nemoćan, treba mu pomoć. — Grandpa is old and frail now; he needs help.
   Dom brine o starim i nemoćnim osobama. — The home takes care of elderly and infirm people.
2. powerless; helpless
   Bili smo nemoćni pred poplavom. — We were powerless against the flood.
   Policija je bila nemoćna da spreči nerede. — The police were powerless to prevent the riots.

In the sense 'powerless' it is usually used with «pred» + instr. or «da» + verb.