Final answer:
The aluminum rod will expand more than the steel rod when heated, due to aluminum having a higher thermal expansion coefficient. Upon cooling, the rod would contract back to its original length assuming no permanent changes have occurred. The weapon inventor is not considering the complexities and dangers related to controlled thermal expansion.
Step-by-step explanation:
When two rods of different materials, aluminum and steel, with the same length and initial temperature are heated, the rod made of the material with the higher thermal expansion coefficient will expand more. Since aluminum has a higher thermal expansion coefficient than steel, the correct answer to the student's question is A) The aluminum rod will expand more. If the aluminum rod is heated from 300 K to 600 K, it will undergo a greater expansion than the steel rod, and when cooled back down to 300 K, the rod will contract to its original length, given that no plastic deformation has occurred. The amateur weapon inventor who seeks to utilize thermal expansion to launch a bullet is overlooking the need for precise control over the expansion and the resulting safety risks, among other factors. For instance, it is necessary to have a system that allows for the immediate release of pressure that builds up, which could be challenging to create and could also lead to unintended consequences if not properly managed.