Trên một dây đàn hồi dài 1,35m đang có sóng dừng ổn định, có một đầu là một nút và một đầu là một bụng. Tốc độ truyền sóng trên dây là 2m/s. Chu kì của sóng là 0,35.Tính số bụng trên dây

the arctic is a region of the planet, north of the arctic circle, and includes the arctic ocean, greenland, baffin island, other smaller northern islands, and the far northern parts of europe, russia (siberia), alaska and canada.

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