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 man is standing not exactly at the exactly at the centre, in between

1.	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))
Answer» 5 7 6 8 Solution :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.`