Mechanics 2


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Did anyone do this topic today? Im doing further maths and its one of the easier papers. I found it OK, got a bit stuck on the ladder question, finding the coefficient of friction. Also, on the very last question i ran out of time when finding h.

Tom

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Yeah I did ... found it not too bad - got 0.16 if I remember for the co-efficicnet of friction and h was around 15 if I remember - not too bad ... but i messed up the first q.

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This is OCR MEI board right?? Yes it was hard indeed but i used tan72 to get the coeff of friction, somehow you rearrange F=uR to Rsin72/Rcos72 and that cancels out the R and you are left with tan72. I got like 3. something for the u. anyway i dont think i did too bad, i counted my certain marks at the end and it was about 70%. Yeah i didnt have time either to work out h.

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i worked out ive only ost 3-4 marks on the last part (coefficient of friction)

and 1 or 2 marks on the last question (finding h)

its not tan72 lol. mu has to between 0 and 1. I almost worked it out. It was 1/2tan72

1 / (2 tan(72 degrees)) = 0.162459848

You had to resolve the forces and then find R by taking moments about A. (Moment of the weight) - then do muN = friction

blah blah

I think.

Tom

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aaaaaaaaaarg got 0.9 for mu!!! Now you've scared me :|

That mech 1 paper was hard though! Mech 2 as well not as much though. Last question had bitch algebra.

I'll do the question tomorrow in the lesson probably. Should we post it up here for board members to have a go? Come on.

Anyone saved a paper? ;)

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Which question, the ladder one? I can remember it i think.

You've got this ladder, its resting against a SMOOTH, vertical wall (x metres high), inclined to the horizontal at 72 degrees, resting on ROUGH, horizontal ground. The ladder has a weight, W. Draw a diagram showing the forces acting and find a value for the coefficient of friction (mu).

Enjoy :) - first part is easy - 2nd part gets a bit tricky.

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They didn't give you any values for the ladder though - I made up my own but not sure bout whether that would work :s

The tricky question was the one with h though, centre of mass of that composite object. That and the impulse spacecraft question. In fact, the whole paper was hard. Oh well there's still the January retake :p

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Impulse was 75000Ns (J = mv-mu)

Average Force = 1000N

Then the seperate speeds (last part) were 139ms-1 and 149ms-1

I hope

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i worked out ive only ost 3-4 marks on the last part (coefficient of friction)

and 1 or 2 marks on the last question (finding h)

its not tan72 lol. mu has to between 0 and 1. I almost worked it out. It was 1/2tan72

You had to resolve the forces and then find R by taking moments about A. (Moment of the weight) - then do muN = friction

blah blah

I think.

Tom

Actually mu can be above 1!! But I guess at our stage they restrict it. Anyway i did the M1 paper too, God was that hard! I got stuck on the very 1st question you have no velocity or mass and they say work out f=ma!!! Only a distance is given.

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ouch - I did mechs 1 in january and got 95% :)

I was speaking to the standard maths students and they found Mechs 1 really hard aswell - they didnt like the 1st question either :s - but that should mean that the grade boundary goes down.

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Who cares about the grade boundary, ultimately what happens is they add up your marks for all the modules - so it's better to get easier papers on which you score more, then when they add them up you get your high A.

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