The phase angle of a sinusoidal source determines the value of the source at t=0. A sinusoidal source described by the function cos(ωt+ϕ) has a phase angle of ϕ. By convention, the phase angle’s units are usually specified in degrees, because those units are easier to visualize than the units of radians. Changing the phase angle of a sinusoid shifts it left or right along the time axis but has no effect on the magnitude or frequency of the sinusoid. What is the phase angle of the voltage source described as?

Atrain is traveling at 30.0 m/s relative to the ground in still air. the frequency of the note emitted by the train whistle is 262 hz. the speed of sound in air should be taken as 344 m/s. what frequency (f approach) is heard by a passenger on a train moving at a speed of 18.0 m/s relative to the ground in a direction opposite to the first train and approaching it? what frequency (f recede) is heard by a passenger on a train moving at a speed of 18.0 m/s relative to the ground in a direction opposite to the first train and receding from it?