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Homework Help: Easy pressure and fluid problemsi swear

  1. Oct 26, 2005 #1
    easy pressure and fluid problems..i swear :)

    Got some (what I think) are easy pressure and fluid problems.

    A 23.5 kg woman balances on one heel of a pair of high-heeled shoes.The acceleration of gravity is 9.8 m/s^2 :If the heel is circular with radius 0.225 cm,
    what pressure does she exert on the floor? Answer in units of N/m^2.

    On this one I been doing (23.5*9.8)/((.225 x 10^-2)^2*pi) and i get 1448.03 with out the conversion to meters i get 14480348.99 which seems a little high. But 1448.03 is wrong..what am i doing wrong.

    A Ping-Pong ball has a diameter of 1.79 cm and average density of 0.0377 g/cm^3.The acceleration of gravity is 9.8 m/s^2 :What force would be required to hold it completely submerged under water? Answerin units of N.

    On this one I got the volume of the ping ball by 4/3*pi*(1.79/2)^3 which came out to be 3.003 cm^3 and when applying the bouyant force equation of B = p sub f * volume of the object * gravity I get 29429.4 N which comes out to be wrong. Do i need to take that number and multiply it by the area for the force? The numbers seem really high.

    A homogeneous solid object floats on water with 69 percent of its volume below the surface. The same object when placed in a second liquid floats on that liquid with 66 percent of its volume below the surface. Find the density of the object. Answer in units of kg/m^3. Also what is the specific gravity of the liquid?

    On this one i have no idea where to start since it doesn't give me any densities of the liquids other then water which i can only assume to be fresh water with 1.0 X 10^3.

    Any help on these would be great sorta want to learn this stuff and not be doubt with the answers I get are right or not.
  2. jcsd
  3. Oct 27, 2005 #2


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    Homework Helper

    Q1: you're out by a factor of 10. Ans is 14,480.35 N/m²

    Q2: the density of water is 1 gm/cc. The volume of the displaced water is 3 cm^3. So the mass of the displaced water is about 3 gm. Convert that to kg and multiply by g to get the bouyant force

    Q3: sorry, no time to answer.
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