A wooden block begins to slide when an adjustable ramp on Earth reaches an angle of 25∘. The same block–ramp combination is taken to the Moon, where the gravitational field strength is about one-sixth that on Earth. Which of the following best describes the angle at which the block will first slide on the Moon?
a) It will be greater than 25∘, because the weaker gravitational field decreases the component of weight parallel to the plane.
b) It will still be about 25∘, because this angle depends only on the surfaces in contact.
c) It will be less than 25∘, because the weaker gravitational field reduces the normal force and thus the maximum static friction.
d) It will be about 4∘ (roughly one–sixth of 25∘), since the threshold angle is assumed to scale directly with the gravitational field strength.