M1 Edexcel -Dynamics of a particle moving in a straight line

I am doing the question in the attachment and have managed to get the answers to all three parts in the same way as the solution bank. However, for part c) the solution bank say that alternatively consider the cage.

I had 10g down, T up and R(cage) up
then
10g -(T+R) = 10x0.8.
and opposite forces).fact that
What should I be thinking please?

Thanks

You know the tension from an earlier part.
But I think you've got the direction of the normal force wrong, the normal force acts to accelerate the cage (remember Newton's equal and opposite forces, here you are using the fact that the normal force on both objects is equal).

in part b, B's force on A was upwards so the cage's force on B should be upwards shouldn't it?

Yes but we are only interested here in the forces on the cage. Remember that every force has an equal and opposite 'reaction'.

Yes but we are only interested here in the forces on the cage. Remember that every force has an equal and opposite 'reaction'.

I am doing the question in the attachment and have managed to get the answers to all three parts in the same way as the solution bank. However, for part c) the solution bank say that alternatively consider the cage.

I had 10g down, T up and R(cage) up
then
10g -(T+R) = 10x0.8.

What should I be thinking please?

Thanks

I would suggest either uploading the file as a PDF or taking a screenshot of the question from an online solution bank.