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Homework Help: Help Termodynamic problem getting grade tommorow

  1. Nov 8, 2011 #1
    1. The problem statement, all variables and given/known data
    The volume of a m (mass) hydrogen quantity,which wear initially at the temperature t1, increases k times by isobar dilatation.Find: a) L= ? b) the heath Q absorbed. c)Δ U =?

    2. Relevant equations
    How to solve it?

    3. The attempt at a solution

    pv/t=p2v2/t2 ?
    L= p * Δ V ?
    I dont know... and im getting grade tomorrow on it...
  2. jcsd
  3. Nov 8, 2011 #2
    What is the meaning of L?
  4. Nov 8, 2011 #3
    L- mecanic force
    idk how the say it in english

    its the mecanic stuff that in Mecanic phisics is L=f*d and the values are in joules
  5. Nov 8, 2011 #4
    Fxd is called WORK.

    Work is defined as the ...
  6. Nov 8, 2011 #5
    yes i found on wiki english its Work :) but we note it whit L
    so how i do the problem?
  7. Nov 8, 2011 #6
    W= p x V??
    can you tell me what to do?
  8. Nov 8, 2011 #7
    W = force x distance moved

    But Pressure P = Force / Area

    therefore F = P x A

    Hence W = F x d

    = P x A x d

    = P x change in Volume
  9. Nov 8, 2011 #8
    hence your equation for W is correct since the pressure is constant.
  10. Nov 8, 2011 #9
    what A means
    and =P x delta Volume is the equation to fiend W right?
    also how do i fiend the pressure? whit p1/t1=p2/t2?
  11. Nov 8, 2011 #10
    A means Area.

    Use pV = nRT which becomes p1V1/T1 = p2V2/T2 since we assume the number of moles in gas, n, is constant.

    But since the process is isobaric the pressure is constant so that the last equation becomes

    V1/T1= V2/T2.
  12. Nov 8, 2011 #11
    you said earlier that W= P x change in Volume Right?
    so what i do whit v1/t1=v2/t2? as i see nothing that can help in the above
  13. Nov 8, 2011 #12
    W = P x change in volume
    = P x kV1

    Other equation can be used to find final temperature required to find the heat given.
  14. Nov 8, 2011 #13
    and how do i find the p?
  15. Nov 8, 2011 #14
    What physical constants are given numerical values in this problem?
  16. Nov 8, 2011 #15
    m= 2g
    t1=27 celsius=300 Kelvin
  17. Nov 8, 2011 #16
    Is initial volume given a numerical value?
  18. Nov 8, 2011 #17
    It say :The volume of a quantity of Hydrogen of mass m , found initial at the temperature t1, rises of K times in izobare dilatation.Fiend the W ,Q absorbed and the Delta u (Intern energy)
    m=2g t1=27 Celsius and k=2

    For b i think is W=Delta U + Q i think
  19. Nov 8, 2011 #18
    Since k is positive there is an expansion, so work is done BY the system and so heat must enter the system.


    change in U = heat in - work by system.
  20. Nov 8, 2011 #19
    yes bur for W what i do? how i fiend the pressure?
  21. Nov 8, 2011 #20
    I think that some other physical quantity must be given a numerical value.
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