Part (c) is where I have a doubt ...
How do I approach such problems?
They way I approached such problems (and most of them had sufficient friction so that that the block did not move/translate and only toppled) is by finding the torque about the corner, because intuitively, that would be the point about which the block would topple/rotate — it would be the (instantaneous?) axis of rotation.
(My book defines the Instantaneous Axis of Rotation (IOAR) as the point in the body (or extended body) which can be at rest momentarily — Is this definition correct?)
However, that logic broke down (or so the author thinks) in this problem since the corner would no longer be at rest (the cube is translating) and the author decided to calculate torque about a different point.
So, the textbook considers the torque about the c.o.m. of the cube. But, they do not explain how they arrived at the conclusion that we should use the c.o.m. point. This point is not at rest (neither momentarily or permanently) so the IOAR does not pass through it, right?
In other words, how can we decide the point about which we should calculate torque?
Also, let's say we found some good reason to consider torque about the c.o.m. instead of about the corner of the cube. Why doesn't the author (in part (c)) take the torque (about the c.o.m.) of friction into account?
I think I should add (just for reference) pictures of the pages where my book explains IOAR.
^I'm having trouble uploading the second page. Will try again later. Please use this Google drive link to the second picture for now.
Any help will be appreciated. 👍