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A man is standing not exactly at the exactly at the centre, in between two parallel walls separated by a distance 990 m. He fires a gun and hears the first echo after 2 s, the time taken to hear 3rd echo after firing is ______ s. (take velocity of sound in air is `330 ms^(-1)`)A. 5B. 7C. 6D. 8 |
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Answer» Correct Answer - B He hears the first echo after 2 s. The distance between the 1st wall and the man is `d = v xx t = 330 xx 1 = 330 m.` So, the distance between the man and 2nd wall is `990 - 330 = 660 m.` So, time taken for 2nd echo time `= ("distance")/("velocity") = (2 xx 660)/(330) = 4 s` The 3rd and 4th echo reach at the same time. Time taken for 3rd echo = time taken to hear the first echo + time taken to hear the 3rd echo `= 2 + (2 xx 660)/(330) = 2 + 2 xx 2 = 6 s.` |
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