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Edexcel Mathematics: Mechanics M3 6679 01 - 17 May 2017 [Exam Discussion]

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Original post by Heisenberg'sCat
For 6.b) I got 19.2N
The string's total length is stretched to 1m, so T=(16/0.4)*(1-0.6)=24N. Then sint = 0.8 so F=19.2


There are two components of T acting on the particle, so it's 2Tsint = F
Original post by JJSinha
I did the same thing with the hemispherical shell. Used 2πa^3/3 for mass. 6 mark question. I think max 3 lost for this. And maybe 1 for the next one.


If your mass was wrong for the hemi wouldn't you lose a lot more marks I thought? Because I did the same thing and am now kind of panicking as i don't know whether i've done enough to make sure i can get a good mark for this paper...

I had the correct working out and stuff but wrong values for hemi which lead to the wrong value for x bar and theta. idk how many marks i'd have lost or gained.
What did people get for 5 c)? I got (7ag)^0.5 as V{max)
Original post by .floyd.
How many marks was Q6 part c?


6 marks. I forgot to take away the EPE when finding the velocity. How many marks do you think I lost?

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Does anyone know if we get given error carried through marks. I did the correct method for part 7c but my value for w was wrong :frown:
I somehow got l= 1/5 in the second question, have no idea how I did that, and think I used w instead of w squared to find v in the last question. Other than that fairly happy!
UMS/Grade boundary predictions??
Original post by .floyd.
How many marks was Q6 part c?


It was 8 marks not 6!!
Original post by youngar
I somehow got l= 1/5 in the second question, have no idea how I did that, and think I used w instead of w squared to find v in the last question. Other than that fairly happy!
That's right.
Grade boundaries will be high with this one.
Just realised that Q4 I forgot the base.....

I use 11X = 2(4.5a) + 9(2a)(actually have to be 16/9, forgot calculate for the BASE !!)
X = 27a/11 (actually have to be 25/11

so my part b) theta = arctan (11/27) = 22.2 deg. (actually have to be 23.7)

1) How many marks in this question?
2) How many marks I will lose.. as part b depends on a T_T
3) What do you guys think about the grade boundary for a*? probably 70/75 ?
Original post by youngar
I somehow got l= 1/5 in the second question, have no idea how I did that, and think I used w instead of w squared to find v in the last question. Other than that fairly happy!


Wait, it's not 1/5???
can anyone tell me step by step how to solve question 4 part a) ???
Original post by kavindajd
It was 8 marks not 6!!




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For question 4, the centre of masses one with hollow cylinder and hemisphere etc, if I got part a wrong but did correct working for b will I still lose all 3 marks for b?
Original post by l.chislett
Does anyone know if we get given error carried through marks. I did the correct method for part 7c but my value for w was wrong :frown:


Majority of the time yes, they won't penalise you for the same mistake twice. So you should get marks for the method, but not necessarily the mark for the final answer.
Did the cylinder not have a base?I'm pretty sure it did.How may marks should I expect to lose for this error?
Original post by jonahz123
There are two components of T acting on the particle, so it's 2Tsint = F


Ah ****, cheers
Original post by Sapereaude45
Did the cylinder not have a base?I'm pretty sure it did.How may marks should I expect to lose for this error?


It had a base but no top.
The mass of hemispherical shell was on the c1 formula sheet!

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