The best object to use for investigating how gravitational potential energy transforms into kinetic energy is a slide.
In a slide, when an object (such as a person) is at the top, it has gravitational potential energy due to its height. As it slides down, that potential energy is transformed into kinetic energy, which is the energy of motion. This provides a clear and visual demonstration of the transformation of energy types.
The other options (a flat race car track, a spring, and a rug) do not effectively demonstrate this specific transformation of gravitational potential energy to kinetic energy.
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