ocr m1 jan 2012 discussion

hi couldn't find a post on this so i thought i would start one. how did everyone think it went. i thought it went pretty well but no so sure about the last 8 marker. what did everyone get as the answer?

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Reply 1

jammy274

I got 0.75m but I think the answer is 0.90m. I reckon I've got 4 marks for my working.

Reply 2

NightBear

I got 1.03m or something close :/ Oh well.

Reply 3

matthine

I thought it was an okay paper! But everyone else found it hard so maybe that's an indication I ballsed up big time :/
For the 8 mark question at the end I got 1.52m for the greatest height of P. fingers crossed for a few odd method marks at least :biggrin:

but has there ever been a pulley question like that before?!

Reply 4

NightBear

Original post by matthine

but has there ever been a pulley question like that before?!

Not with three weights at different points, no.

Reply 5

amazon123456789

wat did you get for the components question. didnt knw hw to do that

Reply 6

Tommeo

Original post by matthine

but has there ever been a pulley question like that before?!

I got 0.825m for the maximum height. 0.525m where the heavier one pulls it up and 0.3m for where it is decelerating under gravity and where the lightest one still has and effect on it of about a fifth of gravity from memory, (1/4 of the mass??) so I got it to be -7.35ms^-2. I was quite sure about it but because no one else has the same answer I'm a lot less confident now :/ thought it was alright as mechanics papers go tbh. Pretty standard, not as hard as the core 3 one.

Reply 7

hplj

The answer for the 8 mark question was 0.90 m, first 0.525 m then an extra 0.375m

Reply 8

hplj

Original post by amazon123456789

wat did you get for the components question. didnt knw hw to do that

On the last part of the question, the least value was 0 and the greatest value was 43N. It wanted you to change the direction of the forces so that they all act together and then all act against each other.

Reply 9

amazon123456789

Original post by hplj

wat did u gt for the magnitude and bearing?

Reply 10

Xero Xenith

Original post by Tommeo

I wasn't sure that the small one still had an effect - it wouldn't randomly stay taut, would it? :s-smilie:

I thought it was just two stages - taut until R hits, then freefall.

Original post by jammy274

I got 0.75m but I think the answer is 0.90m. I reckon I've got 4 marks for my working.

I got 0.75 as well, which may or may not be right :tongue:

Reply 11

Snowdog94

Original post by Rhiannon3838

I got 0.75 too so hopefully thats right :smile:

Fairly sure it's 0.9m. I spent a while thinking and checking this one :smile:

Reply 12

Mr M

Study Forum Helper

http://www.thestudentroom.co.uk/showthread.php?p=36016680#post36016680

Reply 13

dom20394

Original post by amazon123456789

wat did u gt for the magnitude and bearing?

well thats wrong isn't it ?
if you addd the 15N and the 8N in one direction and take the 20 N you get 3N as the minimum Force

Reply 14

Mr M

Study Forum Helper

Original post by dom20394

well thats wrong isn't it ?
if you addd the 15N and the 8N in one direction and take the 20 N you get 3N as the minimum Force

You can form a closed triangle from these three forces so the resultant is zero.

Reply 15

levantine

Original post by Mr M

You can form a closed triangle from these three forces so the resultant is zero.

its pythagoras triangle you cant just add two sides to give third you do a2=b2 +c2

Reply 16

gufter87

how is it a pythagoras triangle? How does 20 squared equal 15 squared plus 8 squared? Am I being really stupid or something, cos i couldn't get the forces to be in equilibrium. I got 3N as the least magnitude, after trying the 20N force at all sorts of angles, and the resultant coming up greater than 3N each time. Could someone show how you can get a triangle in equilibrium?

Reply 17

levantine

Original post by gufter87

you dont seem to have understood resolving. The hypotaneous is the resultant and you add up all y componenets and x componenets remebering directions

Reply 18

Mr M

Study Forum Helper

Original post by levantine

its pythagoras triangle you cant just add two sides to give third you do a2=b2 +c2

You must have been taught that three forces in equilbrium form a triangle (and it does NOT have to be a right-angled triangle).

Reply 19

Mr M

Study Forum Helper

Original post by gufter87

Presumably you were taught at GCSE how to construct a triangle with sides of 20, 15 and 8? Draw a 10 cm line as the base, set your compasses to 7.5 cm and draw an arc from one end of the 10 cm line, now set your compasses to 8 cm and draw an arc from the other end of the 10 cm line. The point where the arcs cross is the third vertex of the triangle.