A uniform rod of length 0.7 m and mass 10 kg rotates freely about a horizontal axis passing through one end of the rod a bullet of mass 20 g traveling horizontally with velocity v=200 m/s penetrates the end of the rod. and hooked on the rod find the angular velocity of the rod when the bullet hits the bar

neither accurate nor precise.

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

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.