Two metal balls are the same size but one weighs twice as much as the other. the balls are dropped from the roof of a single story building at the same instant of time. the time it takes the balls to reach the ground below will be:
about half as long for the heavier ball as for the lighter one.
about half as long for the lighter ball as for the heavier one.
about the same for both balls.
considerably less for the heavier ball, but not necessarily half as long.
considerably less for the lighter ball, but not necessarily half as long.

Irrigation channels that require regular flow monitoring are often equipped with electromagnetic flowmeters in which the magnetic field is produced by horizontal coils embedded in the bottom of the channel. a particular coil has 100 turns and a diameter of 6.0 m. when it's time for a measurement, a 4.5 a current is turned on. the large diameter of the coil means that the field in the water flowing directly above the center of the coil is approximately equal to the field in the center of the coil. the field is directed downward and the water is flowing east. the water is flowing above the center of the coil at 1.5 m/s . what is the magnitude of the field at the center of the coil? what is the direction of the force on a positive ion in the water above the center of the coil? what is the magnitude of the force on an ion with a charge +e?