Consider a material whose microscopic cross sections in the thermal energy range are:
=2.7⋅10−24 cm2
=9.3⋅10−24 cm2
the density of the material is =19 g/cm3
and its atomic weight is =238 g/mol
the avogadro constant is =6.022⋅1023 mol−1
what is the total macroscopic cross section?
express your answer in units of cm−1

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