The boy, shooting from a slingshot, pulled the rubber cord so that its length became 10 cm longer. What is the speed of a 20g stone? A force of 10 N is required to pull a rubber cord 1 cm. Ignore the air resistance during the flight of the stone.

A detailed solution with a brief note of the conditions, formulas and laws used in the solution, the derivation of the calculation formula and the answer.