Your spaceship lands on an unknown planet. To determine the characteristics of this planet, you drop a wrench from 3.50 m above the ground and measure that it hits the ground 0.809 s later. Assuming that the planet has the same density as that of earth (5500 kg/m3), what is the radius of the planet?

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.