Which of the following is an example of a useful energy change?

The transformation from elastic potential energy to kinetic energy represents a useful energy change because it is a direct conversion that allows the stored energy to do work. When elastic potential energy is stored in a material, such as a compressed spring or a stretched rubber band, it is ready to be released. Once released, this stored energy transforms into kinetic energy, which can then be utilized to produce motion.

In many practical applications, this conversion is essential. For example, in mechanical systems like catapults or slingshots, the potential energy becomes kinetic energy, effectively allowing them to launch projectiles. This straightforward conversion is effective and efficient in harnessing energy for movement.

Other options, such as chemical to heat or electrical to thermal, generally indicate energy transformations that may produce byproducts or are less direct in their usefulness for performing work. Chemical to light is also practical but might not be as universally applicable compared to elastic to kinetic, which is distinctly observable in motion mechanics.