When X-rays of wavelength 0.0630 nm are diffracted by a metallic crystal, the angle of first-order diffraction (n = 1) is measured to be 15.8°. What is the distance (in pm) between the layers of atoms responsible for the diffraction?

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