Four waves are described by the following expressions, where distances are measured in meters and times in seconds. I y = 0.12 cos(3x - 21t)
II y = 0.15 sin(6x + 42t)
III y = 0.13 cos(6x + 21t)
IV y = -0.23 sin(3x - 42t)
Which of these waves have the same period?
A) I and III, and also II and IV
B) I and IV, and also II and III
C) I and II, and also III and IV
D) All of them have the same period.
E) They all have different periods.

Question

Quizplus · Accepted Answer

Waves I and III have the same period because they have the same angular frequency (21 rad/s). Waves II and IV also have the same period because they have the same angular frequency (42 rad/s).

Four Waves Are Described by the Following Expressions, Where Distances