21) A car has an initial velocity of 15m/s. The car slows with a negative acceleration of 4.5m/s^2. How long does it take the car to slow to 4m/s?

Select all of the statements which are true. electrons are located in shells or orbits around the atom. electrons orbit slowly around the atom. electrons travel in one flat path around the nucleus of an atom. the valence of an atom is determined by the number of electrons in the atom's outermost shell.