1. by what are isotopes identified? a. mass numbers b. atomic masses c. atomic mass units d. average atomic masses
and
2. uranium atoms each have 92 protons. how many protons does each u-238 atom have? a.92 b.146 c.238 d.330
and
3. chlorine atoms each have 17 protons. how many neutrons does each cl-37 atom have? a.17 b.20 c.37 d.54

Aplayground merry-go-round has a radius of 4.6 m and a moment of inertia of 200 kg-m2 and turns with negligible friction about a vertical axle through its center. a child applies a 26.0 n force tangentially to the edge of the merry-go-round for 15.0 seconds. if the merry-go-round is initially at rest, how much work did the child do on the merry-go-round?