Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Find the pressure exerted on the mercury?

  1. Feb 14, 2009 #1
    I was working on a problem that stated an airplane is flying at an altitude of 10km. In its nonpressureized cargo bay is a container of mercury 325 mm deep.(the container is vented to the local atmosphere)

    The first part just asked for the atmospheric pressure at 10km. Which I found in a table to be 26.5 kPa. But for the second part it asks to find the absolute pressure at 10km using the the 26.5 kPa and the height of the mercury column.

    My question is how does the mercury column help you with finding the absolute pressure when the problem just says the mercry is sitting in a container? Do I just use ro*g*h to find the pressure exerted on the mercury? I would think there would need to be a height difference in the mercury because of the pressure acting on it.
  2. jcsd
  3. Feb 15, 2009 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Re: pressure

    It probably means, what is the absolute pressure at the very bottom of the mercury.
  4. Feb 15, 2009 #3


    User Avatar
    Science Advisor
    Homework Helper

    Jason03: I agree with the comment by Redbelly98. So you just need to figure out how one computes absolute pressure from gauge pressure, or vice versa. You listed the correct formula for gauge pressure at the bottom of the mercury container. However, did you know g at 0 deg latitude and 10 km above earth sea level is g = 9.7495 m/s^2? I don't know if they want you to use that exact value or just the general constant.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook