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MEI Differential Equations 17/05/13 watch

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    (Original post by NJam)
    From what I remember, I got the same! Thanks for doing this!

    Quick question, 1v), my friend used t=10pi. It seems like we both used t=0. Who is correct? I would've said t=0 because it stated clearly "for this motion".
    Hi, I derived the values x = -0.1 and v = 0.3 from t = 10pi, but for the second differential equation where 2x'' + 3x' + x = 0, I used these values at t = 0 as that is the beginning of this motion.
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    (Original post by borealis72)
    Hi, I derived the values x = -0.1 and v = 0.3 from t = 10pi, but for the second differential equation where 2x'' + 3x' + x = 0, I used these values at t = 0 as that is the beginning of this motion.
    The same as me then . I think we're right!
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    (Original post by borealis72)
    Hi, I derived the values x = -0.1 and v = 0.3 from t = 10pi, but for the second differential equation where 2x'' + 3x' + x = 0, I used these values at t = 0 as that is the beginning of this motion.
    I thought about this and decided on 10pi instead because the current equation was derived from the previous initial conditions, meaning that if you were to use t=0, you would need to do a phase shift, I.e. cos(t+epsilon)+sin(t+epsilon), which is only possible if the time you are using is a multiple of the period (which in this case it is). Something I leant in M3.
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    I did question 1,3, and 4, based on your answers borealis I feel happy with questions 1 and 3, and question 4 you can basically tell you got it all right because of the last part about getting 3sin(t) = e^-3t

    I went from t=0 in the part from 10pi because tbh, I saw that it was 5 marks, and it would get way complicated to find the constants. I did say that the time has started from this point.
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    (Original post by Tedfoo25)
    I thought about this and decided on 10pi instead because the current equation was derived from the previous initial conditions, meaning that if you were to use t=0, you would need to do a phase shift, I.e. cos(t+epsilon)+sin(t+epsilon), which is only possible if the time you are using is a multiple of the period (which in this case it is). Something I leant in M3.

    (Original post by Ldbright)
    I did question 1,3, and 4, based on your answers borealis I feel happy with questions 1 and 3, and question 4 you can basically tell you got it all right because of the last part about getting 3sin(t) = e^-3t

    I went from t=0 in the part from 10pi because tbh, I saw that it was 5 marks, and it would get way complicated to find the constants. I did say that the time has started from this point.
    Seems I might be in the minority then. Tedfoo, I haven't done M3 but I trust your reasoning. I'm not too worried though, method correct and all. Lost 2-3 marks tops there, and I can't see anywhere else.
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    (Original post by Tedfoo25)
    I thought about this and decided on 10pi instead because the current equation was derived from the previous initial conditions, meaning that if you were to use t=0, you would need to do a phase shift, I.e. cos(t+epsilon)+sin(t+epsilon), which is only possible if the time you are using is a multiple of the period (which in this case it is). Something I leant in M3.
    Uh-oh I think you might be right. t = 10pi yields some horrendous constants but looks correct graphically:

    http://www.wolframalpha.com/input/?i...0pi%29+%3D+0.3

    http://fooplot.com/#W3sidHlwZSI6MCwi...wiMS42Il19XQ--
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    (Original post by Tedfoo25)
    I thought about this and decided on 10pi instead because the current equation was derived from the previous initial conditions, meaning that if you were to use t=0, you would need to do a phase shift, I.e. cos(t+epsilon)+sin(t+epsilon), which is only possible if the time you are using is a multiple of the period (which in this case it is). Something I leant in M3.
    I've edited my answer, all it was was a phase shift by 10pi and then you get the same constants that I got haha. Guess it was worth you paying attention in M3.
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    (Original post by borealis72)
    I've edited my answer, all it was was a phase shift by 10pi and then you get the same constants that I got haha. Guess it was worth you paying attention in M3.
    Yeah, another think that went through my mind was that if you used t=0, this would mean that t=10pi WAS the start of the motion. This is not necessarily the case, t=10pi was only an example of a 'large t' where the motion was valid, not necessarily the start of it.:cool:

    Really hope I get above 90UMS in this, but I will be happy with 80. I think my coursework went rather well. What about you guys?
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    (Original post by borealis72)
    Uh-oh I think you might be right. t = 10pi yields some horrendous constants but looks correct graphically:

    http://www.wolframalpha.com/input/?i...0pi%29+%3D+0.3

    http://fooplot.com/#W3sidHlwZSI6MCwi...wiMS42Il19XQ--
    The constants weren't bad if you kept it in pure form: They were multiples of e!
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    (Original post by Tedfoo25)
    Yeah, another think that went through my mind was that if you used t=0, this would mean that t=10pi WAS the start of the motion. This is not necessarily the case, t=10pi was only an example of a 'large t' where the motion was valid, not necessarily the start of it.:cool:

    Really hope I get above 90UMS in this, but I will be happy with 80. I think my coursework went rather well. What about you guys?
    Kind of annoyed now. I did it that way, got the constants in terms of e and thought it was a bit unusual.. then decided to re-do it with t=0. Gutted.

    For uni I need to average 83 in 5 modules this summer, so that's what I'm hoping for! Provided the coursework wasn't disastrous, that should be within my reach.

    What other modules are you doing? Also are you in year 13?
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    (Original post by NJam)
    Kind of annoyed now. I did it that way, got the constants in terms of e and thought it was a bit unusual.. then decided to re-do it with t=0. Gutted.

    For uni I need to average 83 in 5 modules this summer, so that's what I'm hoping for! Provided the coursework wasn't disastrous, that should be within my reach.

    What other modules are you doing? Also are you in year 13?
    I'm currently in Year 13. I did my full A-level in single maths in year 12, in which I did C1-4, M1 and S1. Got an A*

    This year I'm doing M2, S2, M3, FP1, FP2 and DE. Finding Further Maths much more difficult overall, but not as hard as STEP or AEA (thanks be to god).
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    (Original post by Tedfoo25)
    I'm currently in Year 13. I did my full A-level in single maths in year 12, in which I did C1-4, M1 and S1. Got an A*

    This year I'm doing M2, S2, M3, FP1, FP2 and DE. Finding Further Maths much more difficult overall, but not as hard as STEP or AEA (thanks be to god).
    Awesome, congrats!

    Good luck in STEP and AEA! I'm assuming you've applied for maths.. which unis?
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    (Original post by NJam)
    Awesome, congrats!

    Good luck in STEP and AEA! I'm assuming you've applied for maths.. which unis?
    Firm is UCL and insurance is Bristol but I may have to take a gap year and reapply/defer.
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    (Original post by Tedfoo25)
    Firm is UCL and insurance is Bristol but I may have to take a gap year and reapply/defer.
    What's your offer? I'm sure you'll make it!
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    What do you guys wthink the grade boundaries will be this year for an A and a B?
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    I know this is a bit late but for question 4, did anyone remember getting 0 as the value for one of the constants/coefficients for sine or cos?
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    (Original post by hackashaq)
    What do you guys wthink the grade boundaries will be this year for an A and a B?
    probably around 61-63 for an A, 55-57 for B I would think
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    (Original post by hackashaq)
    I know this is a bit late but for question 4, did anyone remember getting 0 as the value for one of the constants/coefficients for sine or cos?
    I do remember getting this


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