Final answer:
The question relates to structural engineering, specifically considering a steel rod's deformation under load and the design considerations for steel and aluminum beams to maintain a constant length difference with temperature changes.
Step-by-step explanation:
The question posed pertains to the field of structural engineering, specifically dealing with the strength and deformation of members in a truss system under load. When considering a steel rod under the weight of a heavy truck, the key factors include the rod's dimensions and the material properties of steel to ensure the rod does not stretch excessively.
To determine the necessary diameter of a steel rod that does not stretch more than 1.0 cm under a 2.5 × 104-kg load, one would apply principles of mechanics of materials such as stress, strain, and the modulus of elasticity.
For the scenario where an engineer designs a structure, requiring a steel beam and an aluminum beam to maintain a constant difference in length regardless of temperature changes, it involves understanding the coefficient of thermal expansion for each material.