1. a speed-time graph shows that a car moves at 20 m/s for 15 s. the car’s speed then steadily decreases until it comes to a stop at 40 s. which of the following describes the slope of the speed-time graph from 15 s to 40 s?
a. linear, sloping downward
b. linear, sloping upward
c. linear, horizontal
d. curved, upward
2.a river current has a velocity of 10 km/h relative to the shore, and a boat moves in the same direction as the current at 10 km/h relative to the river. how can the velocity of the boat relative to the shore be calculated?
a. by dividing the river current vector by the boat’s velocity vector
b. by multiplying the vectors
c. by adding the vectors
d. by subtracting the river current vector from the boat’s velocity vector

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 -