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: Fluid Mechanics

  1. Dec 6, 2004 #1
    I need some help with some review questions for the test. I am trying to check the answers I get with the ones the teacher provided, bit I'm getting stuck. Knowing which equations to use etc... would be really helpful.

    What is the maximum weight an aircraft with a wing area of x m^2 can lift if the air passing beneath the wing moves at y m/s and the air above the wing moves at z m/s?

    Bernoulli's principle I know, but I don't know how to relate it to the wing area.

    A barge with a horizontal cross-sectional area of x m^2 at the water line carries oil with a density z, which is less than that of water. When the oil is loaded the ship goes up y meters. How much oil was delivered?

    I set bouyant force = mg but got stuck

    Suppose a person can reduce the pressure in their lungs to x mmHG below atmospheric pressure. What is the maximum height that water can be drawn up a straw?

    Just need to know how to do these problems. Any help appreciated.
  2. jcsd
  3. Dec 7, 2004 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    1. From the flow velocities, you can find the net upward pressure on the wing (Bernoulli). Multiplying by the area gives the net upward force on each wing.

    2. The product of the cross section and the height tells you the change in the volume of water displaced. Recall the relation (Archimedis) between the density and the volume of water displaced.

    3. Draw a diagram showing a glass of water, the straw with water rising up to some height, h, and the pressures acting at all relevant positions. It's not too hard once you do that.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook