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Unit conversion difficulties on simple problem

  1. Mar 18, 2009 #1
    1. The problem statement, all variables and given/known data

    A 55 g particle is moving to the left at 27 m/s. How much work must be done on the particle to cause it to move to the right at 41 m/s? Answer in joules

    2. Relevant equations



    3. The attempt at a solution

    27-(-41)=68 , 68*55= 3750

    the units here are grams m/s. I need joules. I have no clue on how to make that happen. I can change the g to kg and even get it to newtons (since I know a joule= newton-meter) , but I can't take it any farther. Please help!
     
  2. jcsd
  3. Mar 18, 2009 #2

    LowlyPion

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    Just convert g to kg in your equation is all you need to do.
     
  4. Mar 18, 2009 #3
    I tried that- It gives me an answer of 3.74, but that is wrong. This doesn't really make sense to me.
     
  5. Mar 18, 2009 #4

    PhanthomJay

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    Once you have the correct units, your calculation is nonetheless in error. You have [tex] W = m\Delta v[/tex] , which is the change in momentum, not the work done. What is the correct equation to use for Work?
     
  6. Mar 18, 2009 #5
    oh! The equation I have for work is W=Fx, but all that is given to me is two velocities and a mass. Force is m*a so w=m*a*x. I guess I'm still at a loss here.
     
  7. Mar 18, 2009 #6

    LowlyPion

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    Oops. That's right. I just thought you were converting units wrong like your title was asking.

    Overlooked that it was work and that's not work you have.

    What about figuring the change in kinetic energy then?
     
  8. Mar 18, 2009 #7

    PhanthomJay

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    Are you at all familiar with the Work-Energy equation or Conservation of Total Energy equations??
     
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