Rough endoplasmic reticulum contains ribosomes, while smooth endoplasmic reticulum does not contain ribosomes. The ribosomes are what give rough endoplasmic reticulum its characteristic "roughness."
Potential energy is gaining all the way to the top of the hill due to the increase of height (gravitational pull) on the skateboarder. At the top of the hill potential energy will reach its highest point. Then going down kinetic energy increases as potential energy decreases.
