Question

A 1000 kg car with a speed of 90 km/h brakes to a stop. How many calories of heat are generated by the brakes as a result?

Answer 1

Based on the question, we are going to assume that the energy generated by brakes is going to transform into heat.

$\begin{gathered} E=Q \\ E=\frac{mv^2}{2} \\ E=\frac{1000kg\cdot(\frac{90}{3.6}m/s)^2}{2} \\ E=312500J \\ \end{gathered}$

Now we have to transform J into calories

$312500J=74689.3\text{ }cal$