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Thermal Energy dissapated from brakes.

  1. Oct 25, 2008 #1
    This is another one that I have given several attempts.

    Calculate the thermal energy dissipated from brakes in a 1600 kg car that descends a 20 degree hill. The car begins braking when its speed is 95 km/h and slows to a speed of 30 km/h in a distance of 0.27 km measured along the road.

    I tried using the conservation of energy equation.


    This doesn't seem to give me what I'm looking for.

    Any help is greatly appreciated
  2. jcsd
  3. Oct 25, 2008 #2


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    You have the correct method.
    Think of it terms of speed and kinetic energy change.
    change in ke + change in pe = energy loss.
  4. Oct 25, 2008 #3
    Just remember to use m/s instead of km/h, and make sure you get the right value for the change in height of the car.

    In your equation, the v and h on the rhs should be different from those on the lhs. Don't use the same symbol for different quantities!
  5. Oct 25, 2008 #4
    Thank you soooo, much. The problem was just that I had the velocity in the wrong units.
    I would have spent forever on that problem!
  6. Oct 25, 2008 #5
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