Un carro de montaña rusa parte del reposo desde una primera cumbre, desciende una distancia vertical de 45 metros y luego sube una segunda cumbre, llegando a la cima con una rapidez de 15m/s. ¿que tan alto está la segunda cumbre? no considere la fricción.

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