Aradioactive nucleus has a half-life of 5 × 108 years. assuming that a sample of rock (say, in an asteroid) solidified right after the solar system formed, approximately what fraction of the radioactive element should be left in the rock today?

Which of the following is an example of units for speed

Asher cycles 12 miles in 16 hours. what is his speed?

Amoving electron has kinetic energy k1. after a net amount of work w has been done on it, the electron is moving one-quarter as fast in the opposite direction. (a) find w in terms of k1. (b) does your answer depend on the final direction of the electron's motion?