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 speed?
A) I and II
B) I and III
C) II and III
D) III and IV
E) II and IV

Question

Quizplus · Accepted Answer

The speed of a wave is given by the ratio of the angular frequency to the wave number. For wave I, speed = 21/3 = 7. For wave II, speed = 42/6 = 7. Both have the same speed.

Four Waves Are Described by the Following Expressions, Where Distances