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Homework Help: Raft acceleration homework problem

  1. May 19, 2008 #1
    A raft is constructed of wood having a density of 600.0 kg/m3. The area of its top surface is 5.7 m2, and its volume is 0.50 m3. When the raft is placed in fresh water having a density of 1.0x10^3 kg/m3, how much of it is below water level?

    What is the upward acceleration of a helium filled balloon of volume 0.0230 m3 if the mass of the balloon's shell is 0.005 kg? (The density of air is 1.20 kg/m3 and that of helium is 0.177 kg/m3.

    I keep getting the 1st question wrong, I only have one try. I tried Fb=volumexgxdensity

    Then weight=mg=densityxvolumex9.8

    Then I did w/fbx100= %

    then did h=volume/area
    then hx%

    I keep getting it wrong, please help.
  2. jcsd
  3. May 19, 2008 #2


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    Staff Emeritus
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    Gold Member

    The weight of the raft is supported by the weight of the volume of water displaced. So you have to equate the weight of the raft with the equivalent of water to find the volume of water displaced. You should then be able to work out how much of the raft is submerged.
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