Why do we always only see one side of the moon? a. from time to time we see all the sides of the moon from the earth. b. the far (opposite) side only faces the earth during the daytime when the sun’s light outshines the moon. c. the moon is tidally locked with the earth. d. the moon does not rotate.

Engines for propeller-driven aircraft are limited in their maximum rotational speed by the fact that the tip speed of the propeller must not approach the speed of sound in air (mach i). taking 6 ft as a typical diameter for a propeller of a light airplane and 1100 fils as the speed of sound, find the upper limit on the rpm (revolutions per minute) of the propeller shaft.