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Homework Help: Need Help before a test

  1. Aug 28, 2010 #1
    Acceleration is related to velocity and time by the following expression: A=V^pT^q. Find the powers p and q that make this equation dimensionally consistent. I already got the answer.I guessed and got lucky
    Could someone tell me how to get the answer step by step
    Please and Thank You
     
  2. jcsd
  3. Aug 28, 2010 #2

    rock.freak667

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    Last edited by a moderator: Apr 25, 2017
  4. Aug 28, 2010 #3
    I thought I understood it but I guess i didnt
     
  5. Aug 28, 2010 #4

    rock.freak667

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    Well post your work up to where you got confused.
     
  6. Aug 28, 2010 #5
    The exponents from when u posten last time was 2 and -1 where did those come from
     
  7. Aug 28, 2010 #6

    rock.freak667

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    Ah, remember your rules of indices?

    A= L/T2 = LT-2

    V=L/T=LT-1

    t=T

    So you'd have

    LT-2= (LT-1)p(T)q

    Remember these rules:

    (ab)n=anbn and (an)m=amn and that (an)(am)=am+n

    It is just applying those rules.
     
  8. Aug 28, 2010 #7
    whats indices I dont remember that?
     
  9. Aug 28, 2010 #8

    rock.freak667

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    Last edited by a moderator: Apr 25, 2017
  10. Aug 28, 2010 #9
    so will the answer alway be 1 and -2
     
  11. Aug 28, 2010 #10

    rock.freak667

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    No you need to simplify the terms on the right side of the equation until you just have one L and one T on the right.
     
  12. Aug 28, 2010 #11
    I get it now you get the negative by dividing the numbers and subtracting the exponents
     
  13. Aug 28, 2010 #12

    rock.freak667

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    Well not by subtracting, but by the rule that 1/an=a-n
     
  14. Aug 28, 2010 #13
    Ok I think I get it now, now i hope he gives us a practice problem before the test

    Thank you again
     
  15. Aug 28, 2010 #14

    rock.freak667

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    You could try this problem and say what you got for 'p' and 'q'.
     
  16. Aug 28, 2010 #15
    what problem the one I just gave as an example
     
  17. Aug 28, 2010 #16

    rock.freak667

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    Try S=Aptq

    Where S= displacement/distance , A = acceleration and t= time.
     
  18. Aug 28, 2010 #17
    So is S= [L]
     
  19. Aug 28, 2010 #18

    rock.freak667

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    Yes.
     
  20. Aug 28, 2010 #19
    So the equation is:
    [L]=[L]/[T]^2*[T]^2
     
  21. Aug 28, 2010 #20

    rock.freak667

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    Right, now simplify the right side.

    EDIT: you forgot the powers 'p' and 'q'
     
    Last edited: Aug 28, 2010
  22. Aug 28, 2010 #21
    would the right side be four(4)
     
  23. Aug 28, 2010 #22

    rock.freak667

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    uhm no, you need to simplify the right side

    (L/T2)p(T2)q such that you will have just one L and one T i.e. group all the Ls and all the Ts together.
     
    Last edited: Aug 28, 2010
  24. Aug 28, 2010 #23
    im sorry to be taking up all ur time

    so u would combine like terms [T]
     
  25. Aug 28, 2010 #24

    rock.freak667

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    Yes you would. So the L on the right would just become Lp, what does the T become?
     
  26. Aug 28, 2010 #25
    T^q i think
     
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