I do not fully grasp the concept behind all of these sub questions (i)-(iv).
Friction Force = Coefficient of Friction * Normal Force
The Attempt at a Solution
(i) Varying as simple harmonic motion sees varying acceleration as it oscillates forwards, until a stationary point and then backwards.
(ii) Same (not varying) as block A moves with block B, in identical harmonic motion?
(iii) I think this has to do with the result of (ii), which would indicate (ii)'s correct answer is 'varying' but I am not sure why (conceptually).
(iv) as (iii)