Chapter 14, Problem 6P

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?

To determine

Energy generated when brakes are applied

Answer to Problem 6P

Solution:

Energy generated when brakes are applied is 452642 J or 10.813 kcal

Explanation of Solution

Given:

$v$ is 95 km/h

$m$ is 1300 kg

Formula Used:

The formula used is kinetic energy

$T=\frac{m}{2}{v}^2$

Where,

$T$ is the kinetic energy

$v$ is the velocity

$m$ is the mass

Also the conversion formula is need: 1000 Calories is 4186 J

Calculation:

$v$ is 95 km/h

The conversion of km/h is done by $\frac{5}{18}$

When $v$ is 95 km/h it can be converted using $95\frac{5}{18}=26.4$ m/s

$v$ is 26.4 m/s

Inserting the given values in the kinetic energy formula: $T=\frac{m}{2}{v}^2$

$T=\frac{1300}{2}{(26.4)}^2$

$T=452642$ J

If 4186 J is 1000 Calories is, then 452642 J is $452642\frac{1000}{4186}=10813$ Calories or 10.813 kcal