Potential energy of a system increases when work is done
Options:- a) on the system by a conservative force
b) On the system by a non conservative force
C) by the system against a conservative force
Ans is c... explanation??

Consider the example of a ball falling under gravity: work is being done on it by the force of gravity, correct? Does it gain or lose PE as it falls? Now consider a ball that has been thrown upward - does gravity do work on it, or does it do work on gravity? That's enough of a hint - please post back with a complete explanation.