Consider the following scenario: A mass of m is kept on a rough inclined surface of angle of inclination $\theta$. The elevator goes up with a constant velocity v and the block does not slide on the wedge. I need to find work done by frictional force.
When I consider an observer inside the elevator(The elevator is an inertial reference frame), then I find that the work done by friction is zero(since there is no relative motion, and no displacement. However when I consider an observer outside the elevator, I find that:
the work done by friction = (displacement of the elevator)*(component of frictional force in that direction)
This is non-zero.
Why does this difference arise?