1. A radioactive material initially is observed to have an activity of 8000 decays/sec. If nine hours later it is observed to have an activity of 125 decays/sec, what is its half-life? Please give answer in hours, to two sig figs.

2. A proton is accelerated from rest through a potential difference. After acceleration the proton has a wavelength of 980 nm. What is the potential difference responsible for the acceleration of the proton? (Assume non-relativistic speeds.) Upload an image of your work below with your answer clearly labeled.