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Homework Help: PLEASE HELP! 2 questions on thermodynamics I Cant get

  1. Jan 19, 2009 #1
    PLEASE HELP! 2 questions on thermodynamics I Cant get!!

    I have an assignment in Physics due on wednesday, its on the net and we get three trials to answer the questions, i have gotten all my questions right besides two!! i used up the 2 trials on both, so i dont want to use my third one until im 100% sure!! So im asking you guys hopefully someone can help me!!
    here it goes:

    At a fabrication plant, a hot metal forging has a mass of 76.5 kg and a specific heat capacity of 448 J/(kg C°). To harden it, the forging is quenched by immersion in 780 kg of oil that has a temperature of 38.4 °C and a specific heat capacity of 2630 J/(kg C°). The final temperature of the oil and forging at thermal equilibrium is 50.2 °C. Assuming that heat flows only between the forging and the oil, determine the initial temperature in degrees Celsius of the forging.

    2)A rock of mass 0.445 kg falls from rest from a height of 20.1 m into a pail containing 0.468 kg of water. The rock and water have the same initial temperature. The specific heat capacity of the rock is 1880 J/kg C°. Ignore the heat absorbed by the pail itself, and determine the rise in the temperature of the rock and water in degrees Celsius.

  2. jcsd
  3. Jan 19, 2009 #2


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    Re: PLEASE HELP! 2 questions on thermodynamics I Cant get!!

    For (1) did you use the idea that: The heat gained by the water = The heat lost by the forging ?

    For (2) Don't you think that the kinetic energy of the rock just before it hits the water gets converted into internal energy of the water+rock. Therefore you should think of the conversion of K.E. into heat?
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