ERRATA: for Q13 (at 5:07) and q20 the answer is B (which I say), but due to an editing error I circled D in both cases. Apologies

Thanks Paul, our exam was a gift tbh

Okay dokey, thanks for this. Q20 needs discussing on a few levels. a) It contains ideas from rotation which is STRICTLY not in the syllabus. b) Length contraction? AT A POINT? Since when does a point contract. More on this later. Q20 should be tricky, but should not contain ideas from outside the syllabus AND suggest that a a point can experience" length contraction". This question just wasn't checked properly in terms of examining if it is is the syllabus and should never have gotten past the important step of whether or not the PHYSICS is correct. Students are NOT taught that the instantaneous velocity of a tyre is zero at point of contact- certainly not in this syllabus,( although I suspect that many will be taught this nest year in response to a situation where the exam sets the syllabus). That a rolling wheel ( and I note the examiner was smart enough to include no slipping - its a pity they didn't check that the content was examinable, however) is the combination of a CW SPINNING wheel - (YES THIS IS ON THE SYLLABUS, as this is just regular ucm) - and a TRANSLATION of the wheel to the right. Combining both the liner translational velocity PLUS the tangential velocity of the points P Q and R of course allows this not known fact for year 12 physics students to be easily shown. ie the velocity of a tyre, wheel etc is zero at pt of contact, equal to v at the centre of mass and 2v at the top of the wheel. This is not intuitive and is not part of the current physics syllabus since the rotation elective was removed in 2001. Either the examiner believes that students can discover this in an exam situation - INCORRECT and simply poor passement OR They believed it is a legitimate question to ask based on the syllabus - INCORRECT. As evidenced by your statement, with no explanation, that the "wheel is not moving at P". Your velocity vector for point R ( upwards!!!) was also unconvincing. Its tangential ie towards the right and should be twice the length of the labelled vector of 0.4 c b) Although you alluded to the idea of a point, it is just embarrassing that the question was asked at all. What would our mathematical friends think? Points cant change in length because they have no length. Good exam MC questions are hard to set, and by and large NESA sets some outstandingly good questions over the years,, clever thoughtful and which can also produce good discourse amongst physics teachers. This is not one of these questions. You also do a fantastic job of providing excellent suggestions in how to answer these questions. So thank you for all of your fantastic work. On this occasion, I was disappointed. If you are independent from NESA why don't you call them out occasionally when they write such awful questions? In terms of the physics involved and the ineptitude in asking questions which ought not to be examined from a prescribed syllabus perspective, I'm afraid this question is indefensible.

Thanks mate you're a legned.

#13

#20

hey mate, big mistake at 5:20. You circled the wrong answer as correct.