The number of radioactive decays in a given sample of radioactive material during a ten year period will be: a certain fraction of all the radioactive atoms in the sample all the atoms with halflife less than 10 years none of the atoms all of the atoms o a certain number of atoms

Two 2.0-cm-diameter disks face each other, 1.0 mm apart. they are charged to ±10 nc. what is the electric field strength between the disks? a proton is shot from the negative disk toward the positive disk. what launch speed must the proton have to just barely reach the positive disk?