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In answering A) I found the 600N downwards force (weight) and 900N upwards force (magnetic). But apparently there's also a 300N normal contact force acting downwards, from the magnet, on the fringe as well. Why? How was I supposed to find it?

It also comes up for B) as a 300N contact force acting upwards on the magnet. Why?

++ It says the tension pulling it all up is 1000N, how could I have found this? I tried making to make upwards forces = downwards forces, but that didn't work.

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    Constant speed implies net force is zero, hence the normal reaction to balance forces. Also, this is a question for http://physics.stackexchange.com/ , not this site. – 2017-01-16
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    @stochasticboy321 sorry, I'm doing this as a part of a maths course not physics - I'll post it on the physics site next time though! – 2017-01-16
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    Yeah, that was more so that in general you know there's a stackexchange entirely devoted to this kind of questions. Anyway, once you buy that there's a normal force pushing down on the fridge, the third law tells you there's a normal force of equal magnitude pushing up on the magnet. The tension on the string has to balance the net downward force in the system, again since the system is moving at a constant velocity. – 2017-01-16
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    @stochasticboy321 ah it adds up now, cheers! – 2017-01-16

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