Question

Can someone please explain this to me? There are no calculations involved. I just need to give a sound explanation.

Answer 1

a) acceleration is defined as change in velocity, velocity is a vector quantity, since it is changing direction constantly (velocity is changing), the acceleration will not be zero.

Answer 2

a=correct :)

Answer 3

b)

Let us consider the work done (for applied) by the engine is constant on both paths. On path DE, you have to overcome frictional force as well as it's weight, i.e.
Applied force - Mgcos\(\theta\) - Friction <-- will be causing the acceleration

while on path EF, your Mgcos\(\theta\) vanishes, so you have greater force, which shows it's velocity is increasing.