4. On Saturday. raggie had 16 minutes
remaining on his cell phone plan. He used 1/2
of those minutes calling his mother. He talked
to his friend for another 5 minutes. After he
made those two calls, how many minutes did
he have left?

Man i dont know this answer

The velocity would be 2 

Ithink about 50 % of an original isotope's number of atoms remain

Vander waals forces are inter molecular bonds that exist within molecules of the same substance. a water molecule is made up of oxygen and hydrogen atoms which share electrons between each other. the vander waals forces are forces that exist between multitude of different  molecules of water. dipole dipole forces is the type of vander waals force that exist in water. the oxygen atom which is more electronegative pulls the shared electron closer to itself thus generating a partial negative charge while the hydrogen acquire a partial positive charge. these two different charges causes attraction to occur in water molecules.