1. In M1, why do we assume that the strings are light and inextensible? I've been told that assuming that it's inextensible guarantees common acceleration but I can't see why. As for light, I've seen two different explanations that both make sense to me one is that it being light lets you treat the mass term in F=ma as zero, meaning that the string must be in equilibrium, making tension problems far easier. The other explanation I've seen is that if the string is light, we don't have to worry about it's mass causing anything to accelerate.
2. I wanna quickly check the whole thing with modules being swapped between maths and further maths, can modules which are ladled as A2 be swapped with modules that are ladled as AS? I've been told that to get an A* in further, you need to average 90% over 3 A2 modules and get a A overall but what would happen if say for example you say FP2, M2 and M3 but didn't score highly enough for either an A or an A*? Could they then swap something like M1 from normal maths to give you an A in further? (of course, this assumes that the swap doesn't effect your maths grade and that the M1 mark is sufficient, and I'm under the impression that FP2 cannot be swapped).