Sound of a certain wavelength is coming from within a room and passing through a rectangular door (a "slit"). If the width of the doorway is twice the wavelength of the sound, what is the diffraction angle of the sound leaving the doorway?

The period of a pendulum varies directly as the square root of the length of the pendulum and inversely as the square root of the acceleration due to gravity. find the period when the length is 144 cm and the acceleration due to gravity is 980 cm per second squared, if the period is 7pi seconds when the length is 289 cm and the acceleration due to gravity is 980 cm per second squared.