What is the output RPM of the gearbox in an APU?

The output RPM of the gearbox in an Auxiliary Power Unit (APU) is typically around 60,000 RPM. However, in specific contexts such as in a question with provided choices, it’s important to focus on what the question may be referring to regarding a more practical or operational RPM that engines or APUs may have, which can differ.

In this case, if the correct answer is indicated as 6000 RPM, this figure may represent the output speed of an APU that is coupled with an application that requires reduced operational speeds for various accessories or systems, rather than the maximum output of the APU itself.

The chosen RPM allows for the operation of electrical generators or pneumatic systems linked to the APU, fitting within the operational parameters expected for compatibility with the connected systems. This speed balances functionality with the mechanical needs of aircraft systems using the APU as a power source.