I’m in the thick of marking exam papers. In physics, a lot of what a student does is mathematically based, so a fair bit of any exam is going to contain calculations of things. But don’t think that it is compulsory to make your answer totally incomprehensible.
Many of the exam answers I see from students look like the result of a twisted experiment involving Sudoku and Scrabble. Letters and numbers are strewn around the page in a fairly random manner, occasionally with an equals sign that may or may not be in the right place. Units are always conspicous by their absence. Such a scrawl is really really hard to mark. Your reasoning, in your head, might be perfect, but unless you can get it down onto the paper in a comprehensible manner it might not be getting you much credit.
So please, put in a few well chosen words. For example, you can say ‘taking moments about point O gives…’, or ‘using conservation of energy we have…’ rather than launching straight into the equation. Remember, if the examiner can’t work out what on earth you are doing, your chances of getting credit for it are on a par with those of New Zealand winning the rugby world cup.