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Homework Help: Buoyancy and mechanical energy

  1. May 2, 2007 #1
    1. The problem statement, all variables and given/known data
    A block of unknown material weighs 50 N in air and 20 N in water. What is the buoyant force of water?

    2. Relevant equations
    I know how to calculate density etc. I thought the formula to use was -density x V x g but it's not correct.


    1. The problem statement, all variables and given/known data
    A x Kg mass is attached to a horizontal spring of constant 20 N/m and set into harmonic motion with an amplitude = 0.2m. What is the total mechanical ernergy of the system?

    I have no idea what to do... Some help would be greatly appreciated. Thanks!
     
  2. jcsd
  3. May 2, 2007 #2

    Mentz114

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    Gold Member

  4. May 2, 2007 #3
    I was thinking it would be 50 - 20 = 30 but it seems a bit too simple to be true...
     
  5. May 2, 2007 #4
    So for the second:
    0.5 * 25 * 0.2^2 = 0.50J ?

    THANK YOU!
     
  6. May 2, 2007 #5

    Mentz114

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    Gold Member

    It's simple and it's true.

    I can't check your second answer because I can't see what the mass is.

    [edit] E = 1/2ka^2 - whoops, you don't need the mass, so you're right there also.
     
    Last edited: May 2, 2007
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