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Homework Help: Fluid Mechanics - find a cavity of a block if it exist?

  1. May 24, 2012 #1
    1. The problem statement, all variables and given/known data

    You are given a 10cm Cube of aluminum with Density of 2700kg/m is submerged in water and the weight in water is 13N. If a cavity exist how big is it?

    2. Relevant equations

    The equation i used were B = V * P_water * g to find buoyancy.

    To find the enclosed cavities i used V_0 = V - V_c = B/(p_water * g) - W/(p_m*g)

    3. The attempt at a solution

    for B i did volume of the cube was .1^3 * 1000KG/M for water * 9.8

    and then when plugging in to the equation for enclosed cavities i got
    9.8/(9.8 * 1000kg/m) - 13N/(2700KGM * 9.8)

    from there i got stuck since i got a number that was really small.
  2. jcsd
  3. May 25, 2012 #2
    I prefer to work through stage by stage.
    Can you calculate the upthrust (buoyancy) produced by a 0.1m x 0.1m x 0.1 m in water?
    I think you have calculated the weight of a cube of aluminium, assuming it has no cavity.
    So can you check if there is any difference between the measured weight of the block in water and the predicted weight?
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