This might be out of 4U syllabus but you can do sigma F_y = ma where up is positive then whenever there is a string that is always in tension and when something is in tension it is being pulled away (ie the vector arrow is away from the block) so that means the tension is positive and there is a...
The thing is by the time you try a past hsc paper like 2021 youve heard or seen the "difficult" questions and you have more time to process it so then those questions arent very hard anymore and obviously time pressure in the hsc is a thing
Any tips on how to know what addition or substitution reaction is occuring in reaction pathways, seem to always stuff up on this particularly with the cssa 2021 one