# Suppose a conventional (not electric or hybrid) car is moving at 50 mi / hr then brakes and...

## Question:

Suppose a conventional (not electric or hybrid) car is moving at {eq}50\ \dfrac {mi}{hr} {/eq} then brakes and comes to halt. Once that process is complete, the kinetic energy of the car has been converted to:

a. potential energy.

b. thermal energy.

c. electrical energy.

d. nuclear energy.

## Conservation of Energy Principle:

The conservation of energy principle, also known as the first law of thermodynamics, tells us that energy cannot be created nor destroyed. Any change in energy found in a closed system is caused by either a transfer of energy to another part of the system or to a transformation to another type of energy.

## Answer and Explanation:

Suppose a conventional (not electric or hybrid) car is moving at {eq}50\ \dfrac {mi}{hr} {/eq} then brakes and comes to halt. Once that process is complete, the kinetic energy of the car has been converted to:

a. potential energy.

b. thermal energy.

c. electrical energy.

d. nuclear energy.

If the kinetic energy is used to climb a hill, there will be potential energy. However, since the break was used and no mention of using its position in a gravitational field to stop the car, we can say that the kinetic energy was not converted to potential energy.

When using brakes on a car, the motion of the car is opposed by friction. When friction happens, the kinetic energy of the object, as its molecules bump into the molecules of the other object, passes on its energy as heat. Therefore, the kinetic energy of the car is converted to thermal energy through friction.

If the kinetic energy was used to charge the battery, then it will have been converted to electric energy. Since we are assuming, that like most cars, the car uses friction breaks, thenen we can say that none of the kinetic energy was converted to electrical energy.

Since no fusion or fission reaction was mentioned in how the car was halted, we can assume that the kinetic energy did not turn into nuclear energy.

Therefore, among the four choices, the best answer is b) thermal energy. 