How to how to find diameter dimension equation of of work done

So a diameter is the same as two opposing radii. The formula for the area of a circle is A = π r2, where r is the length of the radius of a circle. We can use our knowledge that a diameter is made up of two radii to understand that r = d/2.

Explanation:

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