Wave Motion 5 Question 13

13. At x=0 how many times the amplitude of y1+y2 is zero in one second?

(2006, 5M)

(a) 192

(b) 48

(c) 100

(d) 96

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Answer:

Correct Answer: 13. (c)

Solution:

  1. At x=0,y=y1+y2=2Acos96πtcos4πt

Frequency of cos(96πt) function is 48Hz and that of cos(4πt) function is 2Hz.

In one second, cos function becomes zero at 2f times, where f is the frequency. Therefore, first function will become zero at 96 times and the second at 4 times. But second will not overlap with first. Hence, net y will become zero 100 times in 1s.



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