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Homework Help: Trying to find volume given newtons/ archimedes principle

  1. Dec 8, 2008 #1
    1. The problem statement, all variables and given/known data

    A paperweight, when weighed in air, has a weight of W = 6.6 N. When completely immersed in water, however, it has a weight of Win water = 4.0 N. Find the volume of the paperweight.

    2. Relevant equations

    Fb = Wfluid

    3. The attempt at a solution

    I can find density using density of object/density of water=weight of object/initial weight-immersed weight

    but can not seem to find out how to find volume... im stuck
  2. jcsd
  3. Dec 8, 2008 #2


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    The difference between the two weights is the weight of the displaced water, isn't it? What volume of water has a weight of 2.6N?
  4. Dec 8, 2008 #3
    I am not sure.. I know that newtons are kg/s^2 I just dont know how it relates in any way to volume
  5. Dec 9, 2008 #4


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    Newton's are kg*m/s^2. They are a unit of force. They have the same units as m*a (in F=ma). Volume relates to mass through density. Mass relates to force through weight equals mg (m is mass and g is the acceleration of gravity). You might want to review some of these topics.
  6. Mar 8, 2010 #5
    The nitty gritty of it is as follows.
    the Difference of the weight in the air, and the weight in the water equals weight of the object
    Therefore, we use the following steps to find the volume of the object.

    Step 1)
    6.6 N -4.0 N = 2.6 N <--weight of water displaced

    Step 2)
    Divide by gravity to get mass of object
    2.6 N / 9.81 m/s^2 = .265kg <-- mass of object

    Step 3)
    Take that and divide by the density of water
    .265kg / 1000kg/m^3 = 2.65E-4 m^3 <--equals the volume of the object
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