For the first one, try drawing the weights of the object in. This will help visualise the forces.
the weights' direction is always in the same direction, downwards. This means that the resultant force will change on the object as it goes round. The force D is given as
D=rmv2But the weight of the object is
mg and always is downwards. in the second picture, the object is at the top but is still held to the drum through centrifugal force.This means
D≥WFor the second one, the only method of energy transfer here is work done against friction. Therefore it is safe to assume that this is true. This is only an assumption, and is stated below that you should give the assumption to the calculation above.
The third one i cant see an 8f) :O sorry if im missing it...
A general point I use is to write as many valid 'marking points' for the question as i can. If the question is worth 2 marks, then 2 points answering that question should be sufficient.