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Some one please help me with the derivation

  1. Feb 6, 2013 #1
    1. The problem statement, all variables and given/known data
    In figure, the pulleys and the cod are light, all surfaces are frictionless, and the cord does not
    stretch.
    a) How does the acceleration of block 1 compare with the acceleration of block 2?
    The mass of block 2 is m2 = 1.3 kg. Derive an expression for the acceleration of the
    block having mass m2 as a function of the mass of block 1, m1.


    2. Relevant equations
    mg-T=m2a2
    T=m1a1=m12a2



    3. The attempt at a solution

    The first one (a) i have done.
    Which is that due to the pulley the acceleration of a2=1/2 a1

    Can some one help me with the b part
     

    Attached Files:

    Last edited: Feb 6, 2013
  2. jcsd
  3. Feb 6, 2013 #2

    NascentOxygen

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    Re: Some one plz help me with the derivation

    Hi lioric. Is there supposed to be a diagram to accompany this?
     
  4. Feb 6, 2013 #3
    Re: Some one plz help me with the derivation

    sorry i was in a rush and forgot
    now its there
     
  5. Feb 6, 2013 #4
    Re: Some one plz help me with the derivation

    This is what i got for the derivation. But something is not right
     
  6. Feb 6, 2013 #5
    Re: Some one plz help me with the derivation

    Mass 2 equation
    The pulley give 2 tensions so 2T
    m2g-2T=m2a2

    Mass 1 equation

    T=m1a1
    since a2 = 1/2a1
    a1= 2a2

    T=m12a2

    substitute mass 1 equation in mass 2 equation as T

    m2g-2(2m1a2)=m2a2
    m2g-4m1a2=m2a2

    make subject a2

    -4m1a2-m2a2=-m2g
    change negative sign by multiplying by -1

    4m1a2+m2a2=m2g

    a2(4m1+m2)=m2g

    a2=m2g/4m1+m2

    But i feel that this is not right.
     
  7. Feb 6, 2013 #6

    haruspex

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    Re: Some one plz help me with the derivation

    It's cog, not cod.
    That equation is not correct. What are all the forces on m2?
     
  8. Feb 6, 2013 #7
    Re: Some one plz help me with the derivation

    m2 would have gravity and tension
     
  9. Feb 6, 2013 #8

    NascentOxygen

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    Re: Some one plz help me with the derivation

    I believe it's c-o-r-d
     
  10. Feb 6, 2013 #9
    Re: Some one plz help me with the derivation

    ok enough about the "CORD"

    m2 would have gravity and tension those are the forces on M2

    so whats next?
     
  11. Feb 6, 2013 #10

    haruspex

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    Re: Some one plz help me with the derivation

    That's better (your post crossed with mine).
    Looks ok to me, if parentheses inserted:
    a2=m2g/(4m1+m2). What bothers you?
     
  12. Feb 6, 2013 #11
  13. Feb 6, 2013 #12

    haruspex

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    The two are equivalent.
     
  14. Feb 9, 2013 #13
    ok thank you
     
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