Abobsled has a momentum of 1500 kg*m/s to the south. air resistance reduces its momentum to 750 kg*m/s to the south. what impulse is applied to the bobsled by the air resistance?

The impulse is exactly the change in momentum,
and they have the same units.

The impulse imparted to the bobsled by the air
resistance is

                       (750 - 1500) = -750 kg-m/s.

It's negative because it reduced the bobsled's momentum.

If the impulse had come from a rocket engine on the back of
the bobsled, then it would have been a positive impulse.

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -

Answerboth technicians (a) and (b);