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

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    Worried about the vertical motion one - hoping I've not made an error.
    Got the proof in part A.
    For part B I put theta=270 into the expression, got V^2 to be 5ag at the top of the circle and then resolved the tension to be 4mg which is larger than zero hence must be complete circles.
    For Part C I said the velocity is max at the bottom of the circle hence put in theta = 90 and got 3root ag
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    Anyone remember how many marks question 3 was worth? I didn't integrate the force with respect to displacement.
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    72 for 90ums?
    69 for 80ums?
    64 for 70ums?
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    (Original post by TrueDAN)
    Worried about the vertical motion one - hoping I've not made an error.
    Got the proof in part A.
    For part B I put theta=270 into the expression, got V^2 to be 5ag at the top of the circle and then resolved the tension to be 4mg which is larger than zero hence must be complete circles.
    For Part C I said the velocity is max at the bottom of the circle hence put in theta = 90 and got 3root ag
    I got those answers but I did part B slightly differently by finding the velocity if it went slack (which was ag) and stated 5ag>ag. Your method seems better - do you think my method is okay?
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    (Original post by Major-fury)
    how did people get 1.02 for the last shm? I thought u would do -0.4=0.5cost(25/3 t ) - find t. and then find the velocity and acceleration for the time the string / slack. I messed up this paper badly I even forgot how to find the mass of a hemispherical shell.... How many method marks would i get for doing everything right but not having the right mass. I messed this paper up so badly even though it was so standard ffs
    If i did all of the method correct for this 8 marker but i messed up finding the velocity (instead of using v^2 = w^2(A^2 - x^2) i assumed all of the epe had turnt to ek hence i got a velocity from there but didnt take in to account that it already had a velocity). I found the right time for whilst it was moving with SHM but not after. How many marks do you think i would drop?
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    (Original post by Major-fury)
    It had a base but no top.
    But wouldn't the center of mass be 27/11a.I have just redone the problem and I arrive at the same answer.Could you tell me where I have gone wrong?
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    (Original post by manoobsmatthew)
    I got those answers but I did part B slightly differently by finding the velocity if it went slack (which was ag) and stated 5ag>ag. Your method seems better - do you think my method is okay?
    So youve proven that it never goes slack, as the velocity is always greater than that achieved if it were to go slack, hence must complete full circles - Id say so yes.
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    For the centre of mass question, if the centre of mass is 16/9 the mass will not be equally devided tho. The bottom prt will have 4.5 recurring
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    how did you do question 3?
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    Can anyone recall how many marks the questions were worth?
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    (Original post by Sapereaude45)
    But wouldn't the center of mass be 27/11a.I have just redone the problem and I arrive at the same answer.Could you tell me where I have gone wrong?
    This is how I did it, sorry for the awful writing but I just did this in paint nowName:  Q4.png
Views: 51
Size:  30.5 KB
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    I think that paper was more deceiving than some people think - I cant see the boundaries being comparable to that of last years.
    Inlcine slope calculus will catch some people out, so will the grim COM with shells, so will the elastic string problem where it doesn't involve any GPE ( I messed that one up and didn't read it fully) and finally then last part of the SHM.
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    (Original post by mario64325)
    This is how I did it, sorry for the awful writing but I just did this in paint nowName:  Q4.png
Views: 51
Size:  30.5 KB
    Yeah that makes sense.How many marks do you think I would have lost?
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    How many marks was question 3b? Was it only two?
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    (Original post by Sapereaude45)
    Yeah that makes sense.How many marks do you think I would have lost?
    Depends where you went wrong, I don't remember the marks for the question (I think it was 4), so probably only 1 or 2, seeing as you seemed to get everything else right
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    Wrote two solutions, one was right one was wrong..... will i get any marks.
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    (Original post by johnlannister8)
    Can anyone recall how many marks the questions were worth?
    1. 7
    2. 8
    3. 7 and 2 ( incline slope calculus)
    4. 6 and 3 (COM)
    5. 4, 6 and 2 (Vertical motion)
    6. 3, 4 and 6
    7. 4, 5 and 8

    Sorry if the order is wrong
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    model anwsers

    https://www.thestudentroom.co.uk/sho...4#post71502464
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    I got (5/2)a for the com question. Didnt take I nto account the mass of the base. I reckon the paper was harder than last years which was 72 for an a*. Therefore I hope its around 70 for an a*
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    (Original post by TrueDAN)
    1. 7
    2. 8
    3. 7 and 2 ( incline slope calculus)
    4. 6 and 3 (COM)
    5. 4, 6 and 2 (Vertical motion)
    6. 3, 4 and 6
    7. 4, 5 and 8

    Sorry if the order is wrong
    Thank-you very much!
 
 
 
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