Question

Estimate the rise in temperature of the brack discs in a car of mass 1200kg traveling at 30m/s which is brought to rest by the application of the breakers alone. The brake discs have a total mass of 5kg. Assume that there is no heat loss and that the marterial of the four brake discs has a specific heat capacity of 800J/kg/k

Answer 1

The entire kinetic energy of the car was absorbed by the disc brakes:

$$KE=Q,\\\space\\ \frac12 Mv^2=cm\Delta t,\\\space\\ \Delta t=\frac{Mv^2}{2cm}=135°\text C.$$