I'm working on a problem for my Grade 11 class. A stone is dropped down a well, and, 16 seconds later, the sound of it splashing into the water is heard by people at ground level. The temperature in the well is 10 degress celsius. I'm asked to find the depth of the well. So, what I've done so far is this... I've said the change in time for the falling rock will be 'y' and the change in time for the sound travelling back up will be '16 - y'. The distance from the top of the well to the point of impact (source of the sound) is 'x'. Given negligible air resistance and whatnot, a = g. The speed of the sound returning up the well will be 332 m/s + 0.6 (10 degrees C), or 338 m/s. I've taken my kinematics equations, and said that, for the falling rock, x = 1/2gy^2, and for the sound travelling up, x = 338 m/s * (16-y). I've set the two equal, but I can't do anything past this point. For some reason, I can't remember the algebraic ... uh, stuff.. that I'd need to do this. I'm thinking I should convert what I have to a quadratic (a + b -c = 0?) and then use the quadratic equation, but I can't remember how to do that. Thanks in advance.