How much spring potential energy is stored when a railroad car spring, k = 3,333 N/m, is compressed 0.20 meters?

Another word for electromagnetic energy is a. heat b. force c. matter d. radiation

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.

Why do atoms emit energy of only specific wavelengths