A ball rolls from rest at the top of a 15.5 m hill, downward to the right and back upward onto a 8.25 m hill. How fast is the ball moving at the top of the second hill?

What do the atoms of elements in the same group have in common? a. they have the same atomic numbers. b. they have the same average atomic masses. c. they have the same number of electron shells. d. they have the same number of electrons in their outermost shells.