Q8. A pendulum has a frequency Of' 5 Vibrations second. An observer Starts the pendulum and fires a gun simultaneously. He hears echo from the cliff after 8 vibrations of the pendulum. If the velocity of sound in air is 340 ms^-1. find the distance between the cliff and the observer. 

Q9. A person standing between the two vertical cliff, produces a sound. TWO successive echoes are heard at 4 s and 6 s, Calculate the distance the cliff  (Speed Of sound in air =320 ms^-1 ) 
[Hint : First echo Will he heard from the nearest cliff and the second echo from the farther cliff.] 

Q10.  A man fires a gun and hears its echo after 5 s. The man then moves 310 m towards the hill and
fires his gun again. This time be hears the echo after 3 s. Calculate the speed Of sound.

Q11. On sending an ultrasonic wave from a ship toward the bottom Of a sea, the time interval between sending the wave and receiving it back is found to be  1.5 s .If the velocity of wave in sea water is 1400 ms^-1. Find the depth of the sea