You drive your car for 2.0 h at 40.0 km/h then for 2.0 h at 60.0 km/h what is your average velocity?

In order to calculate velocity, we'd need to know the straight-line distance between the start and the finish, and we'd also need the direction of that line.  The best we can do with the information given in the question is calculate the average SPEED.

Average speed = (total distance covered) / (time to cover the distance).

Distance covered in the first 2 hours = (2 hr) x (40 km/hr) = 80 km.
Distance covered in the second 2 hours = (2 hr) x (60 km/hr) = 120 km.

Total distance covered = (80 + 120) = 200 km
Time to cover the distance = (2 + 2) = 4 hours

Average speed = (200 km) / (4 hours)  =  50 km/hour

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 -