What is the mass of a moon rock that occupies 250 mL and has a density of 1.02 g/mL?

Asample of silver (with work function ? = 4.52 ev) is exposed to an ultraviolet light source (? = 200 nm), which results in the ejection of photoelectrons. what changes will be observed if: silver is replaced with copper (? = 5.10 ev) more photoelectrons ejected no photoelectrons are emitted fewer photoelectrons ejected more energetic photoelectrons (on average) less energetic photoelectrons (on average)

Which statement best describes the flow of energy in this scenario

The fact that the total amount of energy in a system remains constant is a(n)