Hi guys, thanks for the help given with the last paper I was looking for help with, I think I just may have past that one, however next comes the hard paper, this one is Electrical Systems and there is nothing "Electrical" about it in my view, the entire paper is math theory and the majority of it is trigonometry (with which i am increadibly uncomfortable).

I will start from the beginning with Q2 and Q3 of the paper. (Q1 was simple) any help on what i need to look for and how to manipulate the questions for the answer would be much appreciated, thanks.

Q2:

A circuit breaker is designed to stop fault current flowing in a circuit at a point in time where the current in the circuit is 0.

If the fault curent in the circuit is: Amperes

i) At what time would the first current 0 in the circuit occur?

ii) Given the circuit breaker will take 40mS to operate, at what time would the next current 0 occur after that?

For the first part I am assuming i should make i(t) = 0 so:

Now since I am unsure how one should correctly manipule the cos trig function in this case, i would do the following ... is this correct?:

or should i first have divided both sides by 50 to cancel the 50 out?