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OCR MEI Mechanics 2 (Wednesday 13th May 2015) Watch

  • View Poll Results: What will the A boundary be?
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    (Original post by mathsexam2013)
    by nice i mean the answer was to 1 decimal place
    also do u remember any of the answers to qs4 such as the velocity of q
    Not sure. For the coefficient of restitution I got 7/11.
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    Need to question paper to organise/ give more but here's what I remember putting:

    Loss in GPE was 58.8h
    COM with a=4 and object at B was like y=2.275 and x=1.725 something like that
    S=10N , R = 20sin(theta), F = 20cos(theta) so u=tan(theta)
    P going down slope was like 0.36... m something like that
    The horizontal distance going from 2.5 - bounce - 2.5m was 3m.
    Angle of object with line AB was like 1.7 degrees (did 45-angle from horizontal)
    Power was like 122W at some point in question
    Impulse = -40Ns

    Can't remember any more atm, discuss! xD

    Also, the question where it said show P is at 4ms^-1 in opposite direction, was easy to see it was going 4ms^-1 but how did you prove it was in opposite direction? I just stated it with no prove because I got v^2 = 16 so v=+/-4 ms^-1 so just said "must be -4ms^-1" xD
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    (Original post by joe12345marc)


    Also, the question where it said show P is at 4ms^-1 in opposite direction, was easy to see it was going 4ms^-1 but how did you prove it was in opposite direction? I just stated it with no prove because I got v^2 = 16 so v=+/-4 ms^-1 so just said "must be -4ms^-1" xD
    I think it was about reasoning that the mass and direction of Q were such that P must be going in the opposite direction.
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    It was the opposite to usual. Nice frameworks but bad COM. Looking back should've got the 10 marker. Thought the last part of Q1 was a bit sly. the one for u and tax. Im not sure if it needed a => instead of just a > as didn't specify if it was on the point of tippinng. also, i think that it had to be -4 as if it was +4 it would somehow have to phase through Q which was only going at 3ms-1
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    Vote on the poll everyone....
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    Right. Who put 64 in the poll?
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    Messed up the very end of the 10 marker - got a rounding error that got theta = 0 (which was wrong, obviously, but i didn't have time to continue messing with that one), but I did get the same CoM as most other people (2.575, 1.575). Any ideas on how many marks I could have gotten? I drew the triangle for obtaining the angle properly, just scuffed the final calculation itself.
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    (Original post by Omicr)
    Messed up the very end of the 10 marker - got a rounding error that got theta = 0 (which was wrong, obviously, but i didn't have time to continue messing with that one), but I did get the same CoM as most other people (2.575, 1.575). Any ideas on how many marks I could have gotten? I drew the triangle for obtaining the angle properly, just scuffed the final calculation itself.
    You shouldn't lose more than 3 (two A1's and an M1) i think
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    (Original post by joe12345marc)
    You shouldn't lose more than 3 (two A1's and an M1) i think
    Thank you very much for the reply. Puts me at a little more rest
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    (Original post by joe12345marc)
    Also, the question where it said show P is at 4ms^-1 in opposite direction, was easy to see it was going 4ms^-1 but how did you prove it was in opposite direction? I just stated it with no prove because I got v^2 = 16 so v=+/-4 ms^-1 so just said "must be -4ms^-1" xD
    I said that because Q was travelling at 3ms^-1 in the direction of P's initial velocity, and P's velocity after the collision was 4ms^-1, P can not be going faster than Q in the same direction (it can't simply go through Q), and therefore it must be going in the other direction
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    (Original post by Omicr)
    Thank you very much for the reply. Puts me at a little more rest
    No problem mate anything I can do to help is cool! How do you reckon that paper compared to past papers?
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    (Original post by Omicr)
    I said that because Q was travelling at 3ms^-1 in the direction of P's initial velocity, and P's velocity after the collision was 4ms^-1, P can not be going faster than Q in the same direction (it can't simply go through Q), and therefore it must be going in the other direction
    Aah dammit yeah got that wrong, only 1 mark for explanation though right?
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    (Original post by joe12345marc)
    No problem mate anything I can do to help is cool! How do you reckon that paper compared to past papers?
    Lot harder than last year's, this one was a resit for me (Y13, first go in Y12)

    (Original post by joe12345marc)
    Aah dammit yeah got that wrong, only 1 mark for explanation though right?
    Yeah I think so. Not the worst thing to mess up on - i didn't actually finish the paper on time. Only got part way through the second to last question, completely missed the very last one.

    Speaking of which, how many marks do you think I would have gotten for finding the vertical component of the velocities before and after the bounces? I used SUVAT to get the velocity before, multiplied that by 4/5 for the velocity the other way, and ran out of time there. (again, for second-to-last question)
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    (Original post by Omicr)
    Lot harder than last year's, this one was a resit for me (Y13, first go in Y12)



    Yeah I think so. Not the worst thing to mess up on - i didn't actually finish the paper on time. Only got part way through the second to last question, completely missed the very last one.

    Speaking of which, how many marks do you think I would have gotten for finding the vertical component of the velocities before and after the bounces? I used SUVAT to get the velocity before, multiplied that by 4/5 for the velocity the other way, and ran out of time there. (again, for second-to-last question)
    Sorry could I have some more context please I've completely forgotten that part! (i.e question ish and how many marks?) :P Sorry lol
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    (Original post by joe12345marc)
    Need to question paper to organise/ give more but here's what I remember putting:

    Loss in GPE was 58.8h
    COM with a=4 and object at B was like y=2.275 and x=1.725 something like that
    S=10N , R = 20sin(theta), F = 20cos(theta) so u=tan(theta)
    P going down slope was like 0.36... m something like that
    The horizontal distance going from 2.5 - bounce - 2.5m was 3m.
    Angle of object with line AB was like 1.7 degrees (did 45-angle from horizontal)
    Power was like 122W at some point in question
    Impulse = -40Ns

    Can't remember any more atm, discuss! xD

    Also, the question where it said show P is at 4ms^-1 in opposite direction, was easy to see it was going 4ms^-1 but how did you prove it was in opposite direction? I just stated it with no prove because I got v^2 = 16 so v=+/-4 ms^-1 so just said "must be -4ms^-1" xD

    Thank you, this is making me feel a lot better about how I did
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    (Original post by sarcasmrules)
    Thank you, this is making me feel a lot better about how I did
    Haha no problem!
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    (Original post by joe12345marc)
    Sorry could I have some more context please I've completely forgotten that part! (i.e question ish and how many marks?) :P Sorry lol
    That was the one where you are given that is projected at angle theta (gives you sin theta) at a certain velocity from 2.5m and had to show it bounces back up to 2.5m. It was a 5-marker.
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    (Original post by Omicr)
    That was the one where you are given that is projected at angle theta (gives you sin theta) at a certain velocity from 2.5m and had to show it bounces back up to 2.5m. It was a 5-marker.
    Hmm tough one yeah, I'd assume mark scheme is ish like this based on my answer I gave:
    1 - Resolving velocity prior to collision (I think it was like 7 I can't remember)
    2 - Using coefficient of restitution to find velocity after
    3 - Using SUVAT to find total time
    4 - USING SUVAT with resolved horizontal velocity and total time (or just distance = speed x time lol)
    5 - cao - 3m
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    ICan anyone remember how many marks the last question was worth. There was the question which said show it bounces back up to 2.5m and there was another which said work out the x distance displaces. I think one was 5 and 1 was three but can't remember which way round
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    (Original post by OrangePenguin)
    ICan anyone remember how many marks the last question was worth. There was the question which said show it bounces back up to 2.5m and there was another which said work out the x distance displaces. I think one was 5 and 1 was three but can't remember which way round
    the bouncing back up to 2.5m one was 5 marks and the last part was 3 marks.
 
 
 
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