when work is done on an object, where does the energy used to do the work go?

-- If the work is done to make the object move faster, then
the work done becomes kinetic energy of the object.

-- If work is done on the object but it doesn't move any faster,
then there must be friction holding it back.  In that case, the work
that's done just to keep the object moving becomes heat, in the
places where the friction acts on it.