Question

I have this Question in my book and it doesnt have answers and i have no clue on how to do it.

A 2000 kg vehicle brakes suddenly, reducing its speed from 25.0 m/s to 12.5 m/s, to avoid a pedestrian who has rushed out to cross the street ahead of them. If each of the iron brake drums has a mass of 9.0 kg, determine the rise in temperature in each of the brake drums.
In relation to heat considerations, highlight at least two assumptions you are making to solve this problem?

Answer 1

Brakes work by pressing the brake pads against the brake drum. The friction generated by this mechanism serves to slow the car down. The work done on the car is therefore done by friction and as such, the loss in kinetic energy of the car is given off effectively entirely as heat.

The way you'd solve this problem is to first calculate the loss in kinetic energy of the car. Divide this by four to split the energy among the four brake drums. Assume this energy goes entirely into heat, and determine the rise in temperature of each brake drum via the equation
\[ \Delta E = Q = mC\Delta T\]
m is the mass of the brake drum, C is the specific heat capacity of iron. Q is the energy calculated above. Solve for the change in temperature, and you should be done.

Answer 2

thank you Jemurray3