We can estimate the age of an open cluster of stars by examining

a. the number of stars on the main sequence.
b. the turnoff point of the clusters main sequence.
c. the amount of hydrogen remaining in the oldest star.

How much work would be needed to raise the payload from the surface of the moon (i.e., x = r) to an altitude of 5r miles above the surface of the moon (i.e., x = 6r)?

Which statement best describes copper? a. it has a low resistance and prevents charges from moving freely. b it has a high resistance and allows charges to move freely. c. it has a high resistance and prevents charges from moving freely. d. it has a low resistance and allows charges to move freely

If a simple machine reduces the strength of a force, what must be increased?