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Physics questions

  1. Sep 8, 2005 #1
    I can't seem to find the answer.. can anyone help me please?
    0.5kg of water at 80°C is poured into a copper
    vesselat 10°e. The final temperature of the water
    inthecopper vessel is 70°C and the specific heat
    capacityof copper is 400 J kg-1°C-I.
    (a) Findthe energy loss of the water.
    (b) Findthe energy gained by the copper vessel.
    What do you assume when you obtain the
    (c) What is the mass of the copper vessel?
  2. jcsd
  3. Sep 8, 2005 #2
    This is a chemistry question I believe. Do you know the formula q=mc(delta)t? where q is the energy content in joules, m is the mass in grams , c is the specific heat, and delta t is the change in temperature. Another useful formula is -mc(delta)t=mc(delta)t which is just like what is lost is gained.
  4. Sep 8, 2005 #3
    yep i've heard of the formula but which is which?
  5. Sep 9, 2005 #4


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    Science Advisor

    Which is which??? He just told you what the various letters mean. If you mean whether you are to use it for the water or the copper, the answer is, of course, both!

    The water has gone from 80 to 70 degrees so Δ T is -10. m is given as 0.5 kg and you should know the specific heat capacity of water! Clearly it has lost heat. You use that formula to determine how much heat it has lost.

    The copper has gone from 10 to 70 degrees so its Δ T is 60. It has gained heat. You can't use that formula because you aren't given the mass of the copper. But you can "assume" that whatever heat is lost by the water is gained by the copper (an assumption because you would have to ignore heat lost to the air). That is, after you have answered (a), (b) is trivial!

    After you have that, THEN you can use the formula to determine the mass of the copper.
  6. Sep 10, 2005 #5
    It is a physics question. At least it is in the Hong Kong Certificate of Education Examintion, under the topic heat.
    It is a physical change because no new substance is formed.

    I think it is enough to post the solution as it should be very simple.
    E=energy, m=mass, c=specific heat capacity, (delta)T=change in temperature

    a) E=mc(delta)T
    =21000 J

    b) energy lost by water = energy gained by the copper vessel
    energy gained by the copper vessel = 21000 J
    The assumption is there is no energy lost.

    c) E=mc(delta)t
    m=0.875 kg

    Hope that it is correct.
    Last edited: Sep 10, 2005
  7. Sep 11, 2005 #6
    oh..ok... i'm not thinking clear...sorry... thank you for your help!
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