The role of work and mechanical energy in classical relativity has been a subject of renewed interest in this publication. Here we present a problem that illustrates the relationship between impulse and kinetic energy for a rocket-powered object that can also change its gravitational potential energy. The same introductory physics principles lead to a remarkable result when applied to the mechanics of spaceflight—the Oberth effect—whereby a small impulse can cause a large change in a rocket’s orbital energy without violating any conservation laws.

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