Final answer:
Among the provided options, a rocket launched from Earth is an example of a system whose mass is not constant, as it loses mass in the form of burnt fuel during the launch and ascent, differentiating it from the other choices which have constant mass.
Step-by-step explanation:
The question pertains to the identification of a machine that does not qualify as a compound machine. A compound machine is comprised of two or more simple machines that operate together. Examples include a crane, which combines levers and pulleys, and a train, which integrates wheels and axles. The options provided are:
- a. flagpole
- b. train
- c. pile driver
- e. crane
Among these, the system whose mass is not constant would be a rocket launched from Earth (c). Unlike the other options, a rocket loses mass as it burns fuel during its launch and ascent into space. According to the law of conservation of mass, in an isolated system, the mass remains constant over time. However, due to the expelling of burnt fuel, a rocket does not retain a fixed mass, making it a non-isolated system with variable mass.