Bộ tài liệu bài tập tham khảo môn vật lý bậc đại học bằng tiếng anh Chapter 15 | a The period is twice the time to go from one extreme to the other and v f X X T . or sto two figures. b The amplitude is half the total vertical distance m. c The amplitude does not affect the wave speed the new amplitude is m. d For the waves to exist the water level cannot be level horizontal and the boat would tend to move along a wave toward the lower level alternately in the direction of and opposed to the direction of the wave motion. f X v f v ISOO s x 106 Hz X a X v f 344 m s 784Hz m. b f VX 344 m s x 10 5 m x 106 Hz. a Denoting the speed of light by c X f and m s r rr i m s 0-7 ------ 556m. b ------------------- m. 540x103 Hz 7 Hz a Xmax 344 m s m Xmin 344 m s 20 000Hz cm. b Xmax 1480 m s m Xmin 1480 m s 20 000Hz mm. Comparison with Eq. gives a b c f t _L_ Hz and from Eq. d v ms e x direction. a f v X m s m Hz T f 1 x 10 2 s k 2n X 2n m rad m. b y x t m cos 2nI t Hz -X-- m c m cos 2n s m m cm. d The argument in the square brackets in the expression used in part c is 2n and the displacement will next be zero when the argument is 10n the time is then T 5 - x X 1 Hz 5 - m s and the elapsed time is s e T 2 s. a b a -Ak sin kx mt dx d2 y dx2 -Ak2 cos kx mt dy À d2y 2 . . -Am sin kx mt y -Am cos kx mt dt dt2 1 d y L-2 d y __i _. _ _ -i . r t i _ and so kr andy x t is a solution of Eq. with v m k. dx m dt dy d y 2 b Ak cos kx mt y -Ak sin kx mt dy . . .x d2y 2 . .x -d Am cos kx mt - y - Am sm kr mt and so and y x t is a solution of Eq. with v rn k. c Both waves are moving in the - x -direction as explained in the discussion preceding Eq. . d Taking derivatives yields vy x t -mA cos kx mt and .