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Homework Help: Energy physics homework

  1. Feb 12, 2004 #1
    Help Please!!!

    Hello Could someone help me with this problem? thanks

    A container holds 35.0 kg of water at 20.0 C. HOw much energy must be removed from the water to turn it completely into ice at 0 C?

    The block of ice is projected a cross a surface at an initial speed of 6.50m/s. While it is sliding across the surface, the friction force casues the ice to melt. After the block has stopped sliding and come to rest, how much ice has melted? Assume that all tof the internal enrgy transformed by the frction force goes into the ice -- none goes into the surface.

    With the same assumptions as in part (b), with what speed would the block of ice have to be projected inorder to completely melt it due to friction?
  2. jcsd
  3. Feb 12, 2004 #2

    Chi Meson

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    Homework Helper

    I recognize this question. It's from an AP "B" exam from the early 90's.

    First off, remember that heat is energy. One formula (Q = c m deltaT) will tell you how much heat must be removed to get the water to zero degrees. A second formula (Q = mL) will tell you how much heat must be removed to turn that zero degree liquid water into zero degree ice water.

    Second part: kinetic energy of ice is assumed to turn into heat. HOw much KE? use that amount in that second formula above to see how much mass of ice melts.

    Third. HOw much total KE is needed to melt all the ice? the same as the energy needed to turn the water into ice (second half of the first part). What speed corresponds to that amount of KE?
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