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Homework Help: Distance traveled!

  1. Feb 2, 2010 #1
    1. The problem statement, all variables and given/known data

    A hummingbird has a mass of about 1.7 g. Suppose a hummingbird does 0.15 J of work against gravity, so that it ascends straight up with a net acceleration of 1.2 m/s2. How far up does it move?

    2. Relevant equations



    3. The attempt at a solution

    I don't know what to do with the net acceleration, but i do know you have to convert 1.7 g to kg...
    what would the formula do you use?!
     
  2. jcsd
  3. Feb 2, 2010 #2

    kuruman

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    What does the work-energy theorem say?
     
  4. Feb 2, 2010 #3
    Wnet = delta(KE)
     
  5. Feb 2, 2010 #4

    kuruman

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    Correct. Can you find numbers/expressions for the two sides of the equation?
     
  6. Feb 2, 2010 #5
    (.0017kg)(1.2m/s^2)

    or

    (1/2)(.0017kg)(1.2m/s)^2

    I'm not sure what to do with the Joules
     
  7. Feb 2, 2010 #6

    kuruman

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    What does Wnet mean to you and how do you think you calculate it?

    How about Δ(KE)? What is that all about?
     
  8. Feb 2, 2010 #7
    The Wnet means to me the total work done. and is it Fnet(d)?
    KE = 1/2 mv^2 for Δ(KE)?
     
  9. Feb 2, 2010 #8

    kuruman

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    Correct again. How many different works must be added up to give the total work?
     
    Last edited: Feb 2, 2010
  10. Feb 2, 2010 #9
    is it 1.7(1.2) / .15?!
     
  11. Feb 2, 2010 #10

    kuruman

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    You didn't answer my question. How many different works must be added up to give the total work? In other words, how many forces are doing work here?
     
  12. Feb 2, 2010 #11
    Only 1 force?! the .15 J
     
  13. Feb 3, 2010 #12

    kuruman

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    Force is expressed in Newtons. The 0.15 J is not a force, it is the work done by the bird as stated in the problem. Now think about this: if the bird did not flap its wings and did not exert that force, would it be suspended in mid-air or would something else happen to it?
     
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