Final answer:
The boulder at the top of the hill contains potential energy, which is converted into kinetic energy as it rolls down the hill. Friction between the boulder and the hill converts some of the potential energy into thermal energy. As a result, the boulder rolls only partway up the opposite slope.
Step-by-step explanation:
The boulder at the top of the hill contains potential energy.
Potential energy is the stored energy an object has due to its position or condition. In this case, the boulder has potential energy because it is at a higher elevation, which gives it the ability to do work when it is released. As the boulder rolls down the hill, potential energy is converted into kinetic energy, which is the energy of motion.
Friction between the boulder and the surface of the hill converts some of the potential energy into thermal energy, which is the energy associated with heat. This is why the boulder rolls only partway up the opposite slope.
Learn more about Potential and Kinetic Energy