A glass rod is rubbed with a silk scarf producing a charge of +3.2 × 10–9 C on the rod. (Recall that the magnitude of the proton and electron charges is 1.6 × 10–19 C.) The glass rod has:

not moving. pos accel,

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