I am stumped by the following problem, I can't quite figure out what to do with the information about the speed of sound: A soccer player kicks a rock horizontally off a 31.0 m high cliff into a pool of water. If the player hears the sound of the splash 3.1 s later, what was the initial speed given to the rock? Assume the speed of sound in air to be 343 m/s. I don't think it is implying that the object was traveling at the speed of sound, so I'm not really sure how it figures into the problem, since it does not give a delta X value. The known quantities are delta Y = -31 m and t= 3.1, so using delta Y= Voyt + (1/2)gt^2 and substituting zero for Voy, I solved for t and got 2.525 seconds. Using Vy=Voy + at, I got that Vy = 24.647 m/s. That is where I'm stuck, any advice on where to proceed from here? Thank you for your time!