A 790 kg (1742 lbs) race car travelling at 170 mph (76.0 m/s) is brought to a st

Question

A 790 kg (1742 lbs) race car travelling at 170 mph (76.0 m/s) is brought to a stop by its four massive carbon fiber disk brakes. The work required to stop the race car is equal to the car's change in KE. If all the work were converted to heat, what is the equivalent heat energy in kcal? As opposed disk brakes (rotors and calipers) made of steel, modern race cars use disk brakes made of carbon fiber. Why might this be done? Specific heat capacities (c) of different materials are: c steel, 480. Jmiddotkg-1middotK-1; c pitch-based P100 carbon fiber, 2350 Jmiddotkg-1middotK-1; c rayon-based TC2 carbon fiber, 1850 Jmiddotkg-1middotK-1; and c PAN-based PANEX 33 carbon fiber, 2150 Jmiddotkg-1middotK-1.2 Why do you think the change was made? Which material would you recommend? Why? Each of the four disk brake assemblies has a mass of 20.4 kg. If the temperature at the track is 30.0 degree C, and assuming negligible heat loss from the brakes, find the temperature of the brakes when the car comes to a stop.

Explanation / Answer

1)Heat energy=1/2*790*76^2/4184=545.3Kcal

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