A cyclist is rounding a 20-m-radius curve at 13 m/s . What is the minimum possible coefficient of static friction between the bike tires and the ground

6 cos 34, 6 sin 34 trig

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