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Homework Help: Which one is impossible?

  1. Jun 13, 2010 #1
    1. The problem statement, all variables and given/known data

    Which of the following statements are IMPOSSIBLE? Choose all that apply.

    ___A perfectly functioning hydraulic had a pressure of 36 Pa in the fluid near the small piston and a pressure of 37 Pa in the fluid near the big piston.
    ___A 35 L container displaced 42 L of orange juice when partially submerged.
    ___A substance underwent melting during which its temperature remained constant at 33 °C.
    ___A 37 N brick was fully submerged in water. The buoyant force on the brick was 48 N. As a direct result, the brick was neutrally buoyant.
    ___Last Friday, the Sun heated the Moon via convection.
    ___The temperature inside a vacuum chamber was measured to be 3 °C.



    2. Relevant equations



    3. The attempt at a solution

    Based on what I have learned this is my attempt:

    _x__A perfectly functioning hydraulic had a pressure of 36 Pa in the fluid near the small piston and a pressure of 37 Pa in the fluid near the big piston.
    _x__A 35 L container displaced 42 L of orange juice when partially submerged.
    ___A substance underwent melting during which its temperature remained constant at 33 °C.
    _x__A 37 N brick was fully submerged in water. The buoyant force on the brick was 48 N. As a direct result, the brick was neutrally buoyant.
    _x__Last Friday, the Sun heated the Moon via convection.
    ___The temperature inside a vacuum chamber was measured to be 3 °C.
     
  2. jcsd
  3. Jun 13, 2010 #2
    Try defining temperature in a perfect vacuum.
     
  4. Jun 13, 2010 #3

    kuruman

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    So what is your question? Can you provide reasoning why the ones you marked are impossible?
     
  5. Jun 13, 2010 #4

    kuruman

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    A vacuum chamber does not necessarily hold a perfect vacuum, in fact it never does, not to mention black body radiation.
     
  6. Jun 13, 2010 #5
    You are of course right. I'm too used to idealized questions. :)
     
  7. Jun 14, 2010 #6
    well a vacuum chamber has no air,
    so would it be 0 K meaning their is no motion in the particles...

    so the vacuum one would be impossible too?

    My other question is:
    is this possible:
    A substance underwent melting during which its temperature remained constant at 33 °C
     
  8. Jun 14, 2010 #7

    kuruman

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    I know plenty of vacuum chambers that have air in them. The statement of the question is
    "The temperature inside a vacuum chamber was measured to be 3 °C." There is no mention whether there is gas in it or not. Why do you assume that it contains a perfect vacuum which doesn't even exist?
    What happens to the temperature of a substance when it undergoes a phase transition from solid to liquid? Think of melting ice.
     
  9. Jun 14, 2010 #8
    I asked my teacher about a vacuum chamber today and he said that it contains no air

    and thanks for the other one I understand it now
     
  10. Jun 14, 2010 #9

    kuruman

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    OK. Assume that the vacuum chamber has not even a single molecule of air. You stick a mercury thermometer in it. Originally the thermometer reads 3 oC. Will the mercury column drop and indicate a lower temperaure?
     
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