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How to find acceleration given two masses , an angle ,and kinetic fric

  1. Mar 1, 2013 #1
    Two masses m1=3.2 kg and m2=4.7 kg are connected by a thin string running over a massless pulley. One of the masses hangs from the string , the other mass slides on a 35 degree ramp with a coefficient of kinetic friction uk= 0.30. What is the acceleration of the masses?

    I used 9.81(4.7-3.2[0.3cos(35)-sin(35)]/(3.2+4.7)=7.13 but its wrong
     
  2. jcsd
  3. Mar 1, 2013 #2
    Re: how to find acceleration given two masses , an angle ,and kinetic

    ....wonder if instead of trying to deflect coming asteriods away from earth, if instead we can deflect them towards Venus (similar size planet) so to activate a magnetic field and end its runaway greenhouse effect atmosphere. Two Earths are better than one...of course we would need to get a moon there somehow
     
  4. Mar 1, 2013 #3
    Re: how to find acceleration given two masses , an angle ,and kinetic

    ????????????
     
  5. Mar 1, 2013 #4
    Re: how to find acceleration given two masses , an angle ,and kinetic

    I think (g(m1sen35º-m1cos35ºuk+m2))/(m1+m2) should do the trick.
     
  6. Mar 1, 2013 #5
    Re: how to find acceleration given two masses , an angle ,and kinetic

    would I need to convert to any specific units? like mm to m, g to kg?
     
  7. Mar 1, 2013 #6
    Re: how to find acceleration given two masses , an angle ,and kinetic

    I did (9.81(3.2sin(35)-3.2cos(35)(0.3)+4.7))/(3.2+4.7)=7.13
    and it is wrong
     
  8. Mar 1, 2013 #7
    Re: how to find acceleration given two masses , an angle ,and kinetic

    Does it tell you which mass is on which end of the string?
     
  9. Mar 1, 2013 #8
    Re: how to find acceleration given two masses , an angle ,and kinetic

    yea m2 is hanging at the end of the string
     

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  10. Mar 1, 2013 #9
    Re: how to find acceleration given two masses , an angle ,and kinetic

    No, it gives -6.46, i.e the masses accelerate in the other direction.
     
  11. Mar 1, 2013 #10
    Re: how to find acceleration given two masses , an angle ,and kinetic

    If your saying the answer for acceleration is -6.46 then its wrong.
     
  12. Mar 1, 2013 #11
    Re: how to find acceleration given two masses , an angle ,and kinetic

    Try 6.46?
     
  13. Mar 1, 2013 #12
    Re: how to find acceleration given two masses , an angle ,and kinetic

    that is also incorrect.
     

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  14. Mar 1, 2013 #13

    haruspex

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    Re: how to find acceleration given two masses , an angle ,and kinetic

    You have a sign wrong. Think about which way the forces on m1 parallel to the ramp act.
     
  15. Mar 1, 2013 #14
    Re: how to find acceleration given two masses , an angle ,and kinetic

    I switched cos with sin n I got 8 which is wrong
     
  16. Mar 1, 2013 #15

    haruspex

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    Re: how to find acceleration given two masses , an angle ,and kinetic

    Wrong correction. List the forces acting on m1 parallel to the ramp. What are their magnitudes? Which ones act in the direction of acceleration and which oppose it? What does that make the net force producing the acceleration?
     
  17. Mar 2, 2013 #16
    Re: how to find acceleration given two masses , an angle ,and kinetic

    Oh, sorry, I misunderstood the first post.

    Try this equation for the acceleration:

    (g[-m1sin35°-m1cos35°μk+m2])/(m1+m2)

    It gives 2,58 m/s^2
     
  18. Mar 2, 2013 #17
    Re: how to find acceleration given two masses , an angle ,and kinetic

    can someone please help with my question now?
     
  19. Mar 2, 2013 #18
    Re: how to find acceleration given two masses , an angle ,and kinetic

    Did my equation work?
     
  20. Mar 2, 2013 #19
  21. Mar 2, 2013 #20

    haruspex

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    Re: how to find acceleration given two masses , an angle ,and kinetic

    I agree with that.
     
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