"the total angular momentum of an object changes when a net external force acts on the system." this statement is:
a)always true b) never true c) sometime true, it depends on the force's direction
d)sometime true, it depends on the force's point of application
i can cancel out b). i think the correct answer is a) it doesn't depend on the force's direction or point of application does it?

trig 15.3 cos

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