A soccer player kicks a rock horizontally off a 40m high cliff onto a pool of water.

If the player hears the sound of the splash 3s later, what was the initial speed given to the rock? Assume the speed of sound in air is 343m/s.

Time for rock to hit water = sqrt. (2h/g), = 2.857 secs.
(3 - 2.857) = 0.143 secs.
In 0.143 secs., the sound will have travelled (343 x .143) = 49.049 metres.
Sqrt. (49.049^2 - 40^2) = distance from cliff of 28.3867 metres.
(28.3867/2.857) = initial velocity of 9.936m/sec.