Final answer:
The claim that single-rail ladders should only be used on stable and level surfaces is true to ensure stability and prevent accidents. The statement about the balance scale functioning the same way on the moon is false, however, the scale would still be balanced due to the consistent change in gravitational force applied to both objects.
Step-by-step explanation:
The statement that single-rail ladders are used only on stable and level surfaces is generally considered True. Single-rail ladders, also known as leaning ladders, should only be used where they have firm level ground to ensure stability. In the context of static equilibrium, this means that the ladder can maintain its position without sliding or tipping over.
For instance, in the scenario mentioned in question 12.2 - Is it possible to rest a ladder against a rough wall when the floor is frictionless? - a ladder on a frictionless floor would not be stable, as there would be nothing to prevent it from slipping.
As for the statement in question 17 regarding a balance scale, it is False. On the moon, gravity is not as strong as on Earth. However, since gravity affects both the book and the iron weight equally, the scale would still balance, because the mass of the objects does not change and the ratio of their weights remains the same under a uniform gravitational field.