However - I would just like to validate one thing. You helped clarify for me, that if a force acts in a direction perpendicular to the velocity of *the point of contact* with the object (and not the CoM), than the force does no work on the object.

So can I apply this understanding in the problems I face (solely in order to understand if a particular force does any work) - and then later in the same exercise calculate *total* work done using the method illustrated above (from the book)?

You see what I'm asking? I think that's fine, but I want to make sure. Thanks!