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Homework Help: Quick questions on fluids

  1. Apr 22, 2007 #1
    1. Which of the following is not a unit of pressure? (Points: 1)
    N / m
    mm of mercury

    Well, I would say it's N/m, but I thought it would not hurt to check.

    2. When atmospheric pressure increases, what would hapen to the absolute presure at the bottom of a pool? (Points: 1)
    It does not change.
    It increases by a lesser amount.
    It increases by the same amount.
    It increases by a greater amount.

    It should increase by the same amount, due to Pascal's principle.

    3. Salt water is more dense than fresh water. A ship floats in both fresh water and salt water. Compared to the freshwater, the volume of water displaced in the salt water is (Points: 1)
    the same.
    cannot be determined from the information given.

    I would say it is less, since it is more dense.

    4. An ideal fluid flows at 12 m/s in a horizonal pipe. If the pipe widens to twice its original radius, what is the fluid flow in the wider section. (Points: 1)
    12 m/s
    6.0 m/s
    4.0 m/s
    3.0 m/s

    Do we use: R=v x A ? If so, the answer is 3.0? I am a bit confused here...

    5. A person weighing 900 N is standing on snowshoes. Each snowshoe has area of 2500 cm2 . What is the pressure on the snow? (Points: 1)
    450 N/m2
    900 N/m2
    1800 N/m2
    3600 N/m2

    I have use the equation P=F/A and found the answer to be 3600.

    6. In a hydraulic garage lift, the small piston has a radius of 5.0 cm and the large piston has a raduis of 15 cm. What force must be applied on the small piston in order to lift a car weighing 20,000 N on the large piston. (Points: 1)
    6.7 x 103 N
    5.0 x 103 N
    2.9 x 103 N
    2.2 x 103 N

    I have no idea... Please help me...

  2. jcsd
  3. Apr 22, 2007 #2
    For #1, you got it. N/m is a spring constant unit.
    for #6, you can use this formula F1/A2=F2/A2. I hope that helps!
  4. Apr 22, 2007 #3
    Would A1 and A2 be 3.14 x 5^2 and 3.14 x 15^2?
    Where do I go from there?
  5. Apr 22, 2007 #4
    Oh wait, I took the last answer 2.2 etc and multiplied it by 706.5 then divided by 78.5, and got close to 20,000N. So the right answer it the last one, right? (I did do the conversions though)
  6. Apr 22, 2007 #5
    you got it! area of a circle is PI(r^2)!
    The units are in metres not cm.
    Last edited: Apr 22, 2007
  7. Apr 22, 2007 #6
    Thanks! I chose d) as the right answer. Any idea for the other ones?
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