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Two traveling waves are generated on the same taut string. Individually, the two

ID: 2153042 • Letter: T

Question

Two traveling waves are generated on the same taut string. Individually, the two traveling waves can be described by the following two equations:
y1 (x,t)=(1.49 cm)sin(k1x+(0.348 rad/s)t+Q1)
y2 (x,t)=(5.78 cm)sin(k2x-(9.35 rad/s)t+Q2)
If both of the above traveling waves exist on the string at the same time, what is the maximum positive displacement that a point on the string can ever have?
What are the smallest positive values of the unknown phase constants (in radians) such that the above displacement occurs at the origion x=0 and time t=1.68s.
Q1= (radians) Q2= (radians)

Explanation / Answer

This solution is based on the observation that two sinewaves of equal amplitude but differing phase have a maximum absolute sum where they intersect; this is shown by the fact that their slopes are equal in terms of |dy/dx| at the intersection, and as you move away, the decreasing function has a steeper slope than the increasing one. Any time that happens, you have a maximum sum. So we can say in this case that each amplitude = 0.725A. Then half the phase difference ??/2 = arccos(0.725) = 0.759762 rad; ?? = 1.5195 rad = 87.06 deg = 0.2418?.