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Homework Help: A-Lev Physics Gas and Thermal?

  1. Jan 3, 2009 #1
    Hey folks I been going through past exam papers and got 4 questions which are hard to follow, for those that know please provide a detailed step by step guide. I have completed most of the previous parts of each question which got me some extra values.

    Question 1

    OK heres what I have worked out so far:

    Volume = 5*10^-3
    Mass = 8*10^-3
    Pressure = 900000
    n = 2
    molecular mass = 4
    r.m.s Speed of all molecules = 1300

    Question asks the r.m.s speed of all molecules when the Kelvin temperature has doubled. All I know is that speed is proportional to temperature.

    Question 2

    Should be quick and simple

    Use an ideal gas equation and kinetic theory formula pV = (1/3)Nmc^2 to show the equivalant formula is U = N * (1/2)mc^2

    Question 3

    Pressure = 1.5*10^16
    Density = 1.8*10^5
    r.m.s Speed = 500000
    Number of protons per m^3 = density/proton mass = 1.08*10^32

    Question asks me to calculate the number of moles per m^3 and then the temperature.

    Question 4

    Concerning a water radiator

    Metal sheet dimensions = 0.9*1.5*0.005m
    Solar Radiation arrives at 350W
    Water pumped at (0.45/60)W
    Temp' Difference = 26 - 15 degs = 11 degs
    Mass of water = 1kg
    Heat Capacity = 4200

    Calculate the percentage of solar energy transferred to water.

    Then, using the formula Q/t = -kA(temp diff/x)
    Make a rough estimate of the temperature difference between top surface and bottom of aluminium sheet.

    Any help would be great!
  2. jcsd
  3. Jan 5, 2009 #2


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    Staff Emeritus
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    Homework Helper

    I see that nobody has responded in almost 2 days. Actually there are reasons for this. For one, it's better to post each question as separate threads. Individuals may be able to help you with 1 or 2 questions, but are less inclined to respond when they see all these questions in one thread.

    Not true. However, Kinetic energy is proportional to temperature. That fact, and the relation between speed and kinetic energy, will help here.

    According to our forum rules, you'll need to show an attempt at solving this, or at least give your thoughts on how to start solving it, before getting help. This is another reason why nobody has replied until now.

    (You took a starting stab at Question 1, so I responded with a hint for that one.)

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