How Do Harmonic Waves Create Standing Waves and Affect String Vibrations?

[tanzerino]

1. Two harmonic waves traveling in opposite directions interfere to produce a standing wave described by y=3sin(0.25pi x)cos(10pi t). What is the distance (in m) between the first two antinodes?
4
0.8
2
5
7



assumption 4?


Two harmonic waves are described by

y=4sin(3x-200t)
y=4sin(3x-200t-5)



What is the amplitude of the resultant wave?
4.3
4
8
6.4
5.7
assumption 6.4? as it is 2Acos(phase/2)...



Finally :s
A stretched string is observed to vibrate in four equal segments when driven by a 480 Hz oscillator. What is the fundamental frequency of vibration for this string?

Select the correct answer.
370Hz

120 Hz

245 Hz

619 Hz

494 Hz



assumption 120Hz as f proportional to n
Just tell me if anything is wrong please.thanks in advance.

 

[Interceptor_1]

1st one is 4

 

[tanzerino]

thanks for the help.
anyone can help me check the others?assumptions are my trials