Final answer:
Cross bracing can be used as a midrail or top rail depending on its height relative to the platform, and this statement is true. High-voltage wires are held by insulators but are not wrapped with insulating material, making the statement false. The assumption about the boy pushing a box up a ramp with a force of 100 N is also false.
Step-by-step explanation:
The statement that cross bracing may be used as a midrail or top rail depending on the height at which the rail center sits in relation to the platform is true. In engineering and construction, cross bracing is a technique used to reinforce structures by linking elements diagonally, thereby increasing the structure's ability to withstand forces applied to it, such as in scaffolding, where cross bracing serves the purpose of either a midrail or top rail for the sake of worker safety. The classification of the rail as a midrail or top rail is determined by its height relative to the working platform.
Addressing the other question, high-voltage wires are indeed held aloft by insulating connectors; however, these wires are typically not wrapped in insulating material because the air around the wires serves as a sufficient insulator. Therefore, the statement is false. In the scenario presented about the boy pushing a box up a ramp, it is false to assume that the force exerted is exactly 100 N just based on the dimensions of the ramp without considering the friction and the angle of the ramp.