Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Archimede's principle-related

  1. Jan 5, 2009 #1
    1. The problem statement, all variables and given/known data
    A wooden block floats in alcohol with 3/8th of it's length above alcohol. If it is made to float in water , what fraction of it's length is above water? [Density of alcohol = 0.8 gm/cc]

    2. Relevant equations
    density = mass/Volume

    3. The attempt at a solution

    5/8 of the block is under the alcohol. So the volume of the displaced fluid is 5/8V where V is volume of the block. density = mass/volume so: 0.8g/cc = m/[(5/8)V] m = (5/8) V (0.8g/cc) Then I got the buoyant force -: F = (5/8) V (0.8g/cc) g . After this i create such equation for water with water's density and fraction of block is submerged but how can i relate them :?
  2. jcsd
  3. Jan 5, 2009 #2
    Well the buoyant force will be the same (weight of block doesn't change) but the 5/8 figure will be some thing different, say K.

    (5/8)*V*0.8 = K*V*1.0

    so cancel out the V's and we get

    K = (5/8)*0.8 = 0.5
  4. Jan 6, 2009 #3
    ah yes , duh @ me :|
    Thanks a lot Carid :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook