Q 7

Two waves are described by y_{1} = 6 cos 180t and y_{2} = 6 cos 186t,(both in meters).
With what angular frequency does the maximum amplitude of the resultant wave vary with time?
A)366 rad/s
B)6 rad/s
C)3 rad/s
D)92 rad/s
E)180 rad/s

Q 9

Two point sources emit sound waves of 1.0-m wavelength.The sources,2.0 m apart,as shown below,emit waves which are in phase with each other at the instant of emission.Where,along the line between the sources,are the waves out of phase with each other by radians?
A)x = 0,1.0 m,2.0 m
B)x = 0.50 m,1.5 m
C)x = 0.50 m,1.0 m,1.5 m
D)x = 0.75 m,1.25 m
E)x = 0.25 m,0.75 m,1.25 m,1.75 m