You are here

Question: 

How many joules and kilocalories are generated when the brakes are used to bring a 1300-kg car to rest from a speed of 95 km/h?

Source: Giancoli, Douglas C., Physics: Principles with Applications, 7th Edition, 2014.

Quick Answer: 

$4.5 \times 10^5 \textrm{ J, } 110 \textrm{ kcal}$

Giancoli 7th Edition, Chapter 14, Problem 6

(0:51)

Chapter 14, Problem 6 is solved.

View sample solution

Transcript for this Giancoli solution

This is Giancoli Answers with Mr. Dychko. The kinetic energy of this car is going to get converted entirely into thermal energy, and the amount of heat generated would be equal to its initial kinetic energy. So, that's 1/2 times its mass, 1,300 kilograms, times its initial speed squared which is 95 kilometers per hour times 1 hour for every 3,600 seconds times 1,000 meters per kilometer, and that gives us muse per second here. Square that, and then get about 4.5 times 10 to the 5 joules and converting that into kilocalories multiplied by 1 kilocalorie for every 4.186 times 10 to the 3 joules. And that gives about 110 kilocalories of energy.