A bullet of mass m is fired into a block of mass M initially at rest at the edge of a frictionless table of heighth (as shown in the Figure). The bullet remains in the block, and after impact the block lands a distance d from the bottom of the table. Determine the duration of the projectile motion

i don't know that i agree with that but what's the question ?

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

c) a core temperature of only ten thousand kelvin