Excited hydrogen atoms emit light in the ultraviolet at 2.47x1015Hz. What is the energy of a single photon with this frequency?

2pos suppose an object in free fall is dropped from a building. its starting velocity is 0 m/s. ignoring the effects of air resistance, what is the speed (in m/s) of the object after falling 3 seconds? give your answer as a positive decimal without units. answer here

When balancing a chemical equation:

The number to the right of an element's symbol (ex. c-12) identifies the of an isotope.