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Homework Help: Just these two problems ! I'll be done.

  1. May 29, 2004 #1
    Just these two problems ! I'll be done. :)

    Problem 12.
    Given: specific heat of water = 4186 J/kg degrees Ceicuis
    and water's latent heat of fusion = 3.33 *10^5 J/kg.

    A 0.012 kg cube of ice at 0.0degrees Ceicuis is added to
    0.459 kg of soup at 80.4degrees Ceicuis.
    Assuming that the soup has the same specific
    heat capacity as water, find the final tem-
    perature of the soup after the ice has melted.
    Answer in units of degrees Ceicuis..

    Problem 13.When a driver brakes an automobile, fric-
    tion between the brake disks and the brake
    pads converts part of the car's translational
    kinetic energy to internal energy.
    If a 1610 kg automobile traveling at 28 m/s
    comes to a halt after its brakes are applied,
    how much can the temperature rise in each
    of the four 3.8 kg steel brake disks? Assume
    the disks are made of iron (cp = 448 J/kg *
    degrees C)
    and that all of the kinetic energy is distributed
    in equal parts to the internal energy of the
    brakes. Answer in units of degrees C.

    Note: I really am lost? Need step-by-step help!!!
  2. jcsd
  3. May 30, 2004 #2
    a start: energy is conserved
  4. May 30, 2004 #3


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    Homework Helper

    Problem 12 assumptions:
    - All energy is contained in the ice/soup system. In other words:
    Qice = -Qsoup.
    - Decide whether the final state is the state right at the melting of the last little bit of ice or the state at which the melted ice/soup system attains equilibrium.
    - If you decide that the final state is the former, then assume that the melted ice does not take any energy from the soup. In other words, the melted ice stays at 0o C.

    Then, you have either one or two (heat transfer0) processes to calculate.

    Problem 13:
    They give you the assumptions that you need to make. Use the first law of thermodynamics.
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