photoelectric effect book example

[JustinHorriat_4f]

An example in the book in 1B it says You need to make some estimates of the physical properties involved. The speed of an electron emitted from the surface of a sample of potassium by a photon is 668 km?s21. (a) What is the kinetic energy of the ejected electron?, and in the answer in the book it says that m(e) is 9.109x10^-31 kg, i was just wondering where they got that number from because its no where in the question

[chemboi]

It's a known value, likely to be provided on a test.

[christabellej 1F]

hi! the mass of the electron, as well as the masses of neutrons/protons are on the constants and equations sheet that is on Dr. Lavelle's website. It should also be provided on the test!