A 1500 -kg car is moving at 20.0 m / s. The driver brakes to a stop. The brakes cool off to the

step 1 Here the car ends up in the same thermodynamic state as it started, so it undergoes zero change

A 1500 -kg car is moving at 20.0 m / s. The driver brakes to...

A 1500 -kg car is moving at $20.0 \mathrm{m} / \mathrm{s}$. The driver brakes to
a stop. The brakes cool off to the temperature of the surrounding air, which is nearly constant at $20.0^{\circ} \mathrm{C}$. What is the total entropy change?

Key Concepts

Irreversible Processes and the Second Law of Thermodynamics

Irreversible processes, such as the frictional braking of a vehicle, lead to a net increase in the entropy of the universe. This concept is encapsulated in the second law of thermodynamics, which states that the total entropy of an isolated system can never decrease over time, highlighting that energy conversions are inherently imperfect and accompanied by an increase in disorder.

Entropy

Entropy is a thermodynamic property that measures the degree of disorder or randomness in a system. It is a state function, meaning its change depends only on the initial and final states, and its change during energy transformations helps quantify the inefficiencies and irreversibilities inherent in real processes.

Energy Conversion and Dissipation

When an object slows down due to mechanisms like braking, its kinetic energy is converted primarily into heat as a result of friction. This conversion process is governed by the principle of energy conservation, ensuring that the energy lost from motion reappears as thermal energy, typically increasing the temperature of surrounding materials.

Kinetic Energy

Kinetic energy is the energy an object possesses because of its motion, quantified by the formula one?half times mass times velocity squared. In scenarios where a moving object decelerates, this energy is transformed into other forms, such as thermal energy, which is a fundamental consideration in energy conversion problems.

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