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How does a rolling car convert kinetic energy to potential energy on a hill?

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Study how a series of gears in a waterwheel translates a stream's energy to a millstone — energy conversion Before the Industrial Revolution, power came from three main sources: humans, draft animals, and water.
The ingenuity people used in harnessing waterpower can be seen in this medieval-style mill. The waterwheel is turned by a stream and is connected to a shaft that leads into the building. At the other end of the shaft is a gear. The connection of a series of gears translates the power from the stream to a shaft that drives a millstone, which grinds flour from grain.
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When a car rolls up a hill, it converts its kinetic energy—the energy of its motion—into gravitational potential energy, which is energy stored due to the car's position within Earth's gravitational field.1

As the car ascends, its velocity decreases, causing its kinetic energy to drop. Simultaneously, it gains height relative to its starting point. According to the law of conservation of energy, this kinetic energy is transformed into potential energy, calculated as $m g h$ , where $m$ is the mass of the car, $g$ is the acceleration due to gravity, and $h$ is the change in height.1

In a real-world scenario, some of this energy is also dissipated as thermal energy due to friction and air resistance, meaning not all kinetic energy is perfectly converted into potential energy. If the car were to roll back down the hill, that stored potential energy would be converted back into kinetic energy.12