On a downhill stretch of the road, a driver applies the brakes ofhis car so that he coasts at constant speed. We are interested inthe temperature rise of the brakes. Assume the brakes are made ofsteel and all of the heat generated by friction is absorbed by thebrakes. The hill has a height of 100 m, the car has a mass(including brakes) of 900 kg, the total mass of all brakes is 20kg, and the specific heat of steel is 450 J/(kg ?C).
a) Draw a sketch of the problem and collect the availableinformation.
b) Write down the conservation law that allows you to solve thisproblem.
c) Using the conservation law, the assumption of the problem, and g= 10 m/s2, calculate the heat absorbed by the brakes. (Answer: Q =9x105 J)
d) Calculate the temperature increase of the brakes and the finaltemperature, assuming the initial temperature was 20?C.
e) In the calculation, we assumed that all of the heat generatedduring braking is absorbed by the brakes. In reality, some of theheat is transferred to the environment. Considering this, do youexpect the final temperature of the brakes to be higher or lowerthan calculated?
On a downhill stretch of the road, a driver applies the brakes ofhis car so that he coasts at constant speed. We are interested inthe temperature rise of the brakes. Assume the brakes are made ofsteel and all of the heat generated by friction is absorbed by thebrakes. The hill has a height of 100 m, the car has a mass(including brakes) of 900 kg, the total mass of all brakes is 20kg, and the specific heat of steel is 450 J/(kg ?C).
a) Draw a sketch of the problem and collect the availableinformation.
b) Write down the conservation law that allows you to solve thisproblem.
c) Using the conservation law, the assumption of the problem, and g= 10 m/s2, calculate the heat absorbed by the brakes. (Answer: Q =9x105 J)
d) Calculate the temperature increase of the brakes and the finaltemperature, assuming the initial temperature was 20?C.
e) In the calculation, we assumed that all of the heat generatedduring braking is absorbed by the brakes. In reality, some of theheat is transferred to the environment. Considering this, do youexpect the final temperature of the brakes to be higher or lowerthan calculated?
