1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: Fluids problem

  1. Dec 25, 2006 #1
    I don't have a diagram for this, so I'm going to do my best to describe it.

    A glass tube lying horizontally has three different cross-sectional areas, A, B and C. Area A is 12 cm^2, B is 5.6 cm^2, and C is 6.0 cm^2. Mercury (density = 13,600 kg/m^3) is being pushed through the tube by a piston open to the atmosphere at the end of area A. The mercury flows through area B and leaves the tube at area C with a velocity of 8.0 m/s.

    a) What is the total pressure at point A in area A?
    b) What is the total pressure at point B in area B?

    Relevant equations:

    Pressure = Force/Area
    Density = mass/volume
    A(1)v(1) = A(2)v(2)
    P(1) + (1/2)pv(1)^2 = P(2) + (1/2)pv(2)^2 } part of Bernoulli's equation

    ^all that comes to mind

    My attempt at a solution:

    To calculate the velocity of mercury through area A:
    A(1)v(1) = A(2)v(2)
    .12 m^2 * v(1) = .06 m^2 * 8 m/s
    v(1) = 4 m/s

    To calculate the velocity of mercury through area B:
    A(1)v(1) = A(2)v(2)
    .12 m^2 * 4 m/s = .056 m^2 * v(2)
    v(2) = 8.57 m/s

    I think that the total pressure at point A is just atmospheric pressure (1.013 * 10^5 Pa), but I'm not sure. When I use this value in Bernoulli's equation to calculate the pressure in area B, I get a negative number, which makes me think that my assumption is wrong.
    Last edited: Dec 25, 2006
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted