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!

Find the change in pressure

  1. Feb 25, 2016 #1
    1. The problem statement, all variables and given/known data
    Two balloons are connected by a faucet.
    Gas in the first balloon is at pressure [itex]p_1=100kPa[/itex], and in the second is [itex]p_2=0,5MPa[/itex].
    Volumes are [itex]V_1=0,12m^3[/itex] and [itex]V_2=0,5m^3[/itex].
    Temperature of a gas is constant.
    Find pressure in balloons [itex]p[/itex] after faucet is opened (balloons are not connected).

    2. Relevant equations
    [itex]pV=\frac{m}{M}RT[/itex] - state of ideal gas

    3. The attempt at a solution
    State of gas before before balloons are disconnected is
    [itex]p_1V_1=\frac{m}{M}RT,p_2V_2=\frac{m}{M}RT[/itex]
    and after balloons are disconnected is
    [itex]p(V_1+V_2)=\frac{2mRT}{M}\Rightarrow p=\frac{2p_1p_2}{p_1+p_2}=166,67kPa[/itex].

    Is this correct? How volumes [itex]V_1[/itex] and [itex]V_2[/itex] are not relevant in the equation for [itex]p[/itex]?
     
  2. jcsd
  3. Feb 25, 2016 #2

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Are m and M the same for both?
     
  4. Feb 25, 2016 #3
    Mass of a balloon [itex]m[/itex] and atomic mass [itex]M[/itex] are not given. Could you elaborate how to set the equations
    for finding the pressure [itex]p[/itex] in second case (disconnected balloons)?
     
  5. Feb 25, 2016 #4

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    You can assume M is the same for both, but not m. Assign two different unknowns. You have enough equations to cope with that.
     
  6. Feb 25, 2016 #5
    I'm not sure as I'm only just learning this stuff myself though it appears I'm a couple of weeks behind you but wouldn't it be worth finding the mass flow rate? Sorry if that's wrong.
     
  7. Feb 25, 2016 #6

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    I read the question as asking about the final state, after flow has ceased and temperatures have returned to ambient.
    (Otherwise there is not enough information.)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Find the change in pressure
  1. Changing pressure (Replies: 1)

  2. Change in Pressure (Replies: 4)

  3. Change in Pressure (Replies: 3)

  4. Finding pressure (Replies: 10)

Loading...