1. Not finding help here? Sign up for a free 30min 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!

Work done by the gas

  1. May 30, 2010 #1
    1. The problem statement, all variables and given/known data

    A cylinder is vertically placed with its frictionless ,light and moveable piston facing the top. A mass of known value is placed on it, and its distance from the bottom of the cylinder is known. What is the pressure of the gas ?

    2. Relevant equations



    3. The attempt at a solution

    The potential energy of the mass is the work done by the gas. Since the system is in equilibrium , the gas must do work against the compressing effect of the piston.But the problem is there is no change in the volume of the gas.

    W=p dV is simply zero since dV is 0 . That doesn't make sense ??
     
  2. jcsd
  3. May 30, 2010 #2
    I dont catch it. The question says "what is the pressure of the gas?" and you are considering work.
    Anyway, since the topic is entitled "work done by gas", than there is no work done by gas in this situation. If the gas is compressed, the work is done on it. And since the mass is placed on the piston, the gas is compressed; if the volume changes, it decreases, so that the work done by gas equales 0 no matter what :)
     
  4. May 30, 2010 #3

    ehild

    User Avatar
    Homework Helper
    Gold Member



    Work is done during a process, not in equilibrium. There is no displacement during equilibrium, so there is no work. The gas has to exert force against the compressing effect of the piston.

    ehild
     
  5. May 30, 2010 #4
    Thanks all , so how do i calculate pressure in this case ?

    Also , the volume of the cylinder is also known.

    P=F/A

    F=PA

    where F=mg and A=(volume/height)

    is it just like that ?
     
  6. May 30, 2010 #5
    Yep, it's that simple :)
     
  7. May 30, 2010 #6

    ehild

    User Avatar
    Homework Helper
    Gold Member

    And you are that smart :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Work done by the gas
  1. Work done by a gas (Replies: 6)

Loading...