The count rate of a radioactive source decreases from 1600 counts per minute to 400 counts per minute in 12 hours. What is the half-life of the source?

The sun generates both mechanical and electromagnetic waves. which statement about those wave is true?

In a given chemical reaction, the energy of the products is greater than the energy of the reactants. which statement is true for this reaction?

Awoman stands a distance d from a loud motor that emits sound uniformly in all directions. the sound intensity at her position is an uncomfortable 2.0×10-3 w/m2. at a distance 2.6 times as far from the motor, what are (a) the sound intensity and (b) the sound intensity level relative to the threshold of hearing?