Work done by frictional force in a round trip is not zero.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Friction is a nonconservative force unlike Coulomb force or gravity. It does depend on the path taken from the initial state to the final state.