Question

A car is traveling down a level street at 30 mph. As it approaches a red light, the driver presses the brake pedal. According to the law of conservation of energy, what happens to the energy of the car as it travels from position A to position C?

a) Position C has the most energy because the brakes transformed all of the kinetic energy to thermal energy.
b) Position A has the most energy because the kinetic energy is greatest when the car is moving fast.
c) Position B has the most energy because the car has kinetic and thermal energy while slowing down.
d) The total amount of energy remains the same, but it is transformed from kinetic energy to thermal energy as the brakes are applied.

Answer 1

When a car slows down, its kinetic energy is converted into thermal energy due to friction, consistent with the law of conservation of energy. The total energy remains constant; it just changes from one form to another, specifically from kinetic to thermal.

Step-by-step explanation:

According to the law of conservation of energy, when a car traveling down a level street at 30 mph presses the brake pedal and slows down from position A to position C, the energy of the car is transformed rather than lost. Initially, at position A, the car possesses kinetic energy due to its motion. As the car slows down, this kinetic energy is converted into thermal energy due to the friction between the car's brakes and wheels, which heats up the parts of the car.

Therefore, the correct answer is (d) The total amount of energy remains the same, but it is transformed from kinetic energy to thermal energy as the brakes are applied. The other options are incorrect because the total energy does not increase or decrease; it simply changes form. This transformation occurs because energy cannot be created or destroyed; it can only be transformed from one form to another or transferred from one object to another.