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Homework Help: Specific heat capacity and friction

  1. Nov 28, 2009 #1
    1. The tangential frictional force exerted by a band brakes on a rotating metal drum of circumference 0.25m is found to be 20N. If the mass of the drum is 0.4kg and its specific heat capacity is 0.35 kJ/kg K, calculate the number of complete revolutions of the drum are required to increase its temperature by 5.0 K.

    Q= mcT

    my attempt:

    Q= mc[delta]T

    20d= 700
    revolutions = 35/.25=140 or 1.4*10^2

    ^^^^^is that correct?
  2. jcsd
  3. Nov 29, 2009 #2


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    Science Advisor
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    Gold Member

    No. If you have d, the number of revolutions is not d divided by the radius. It is d divided by the circumference. Also, it is a good habit to show the appropriate units every time you write down a number unless the number is dimensionless.
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