A train is moving at constant speed over a certain period of time. Which of the following statements about the train's motion during this period of time must be false? A. The magnitude of the train's velocity is constant.
B. The distance traveled by the train will be a positive, nonzero number.
C. The train's direction of motion may change.
D. The instantaneous speed may be higher or lower than the average speed.

if the person is shown to have +90n, then ans is -10n.

if the person is shown to have -90n, then ans is +10n.

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me