Motion in a straight line HELP!!!! Here's my problem... A rock is dropped (from rest) from the top of a 87.5-m-tall building. How far above the ground is the rock 1.2 s before it reaches the ground? .....so far this is what I came up with y=(1/2)gt^2 t=sqrt(2y/g) = sqrt((2*87.5)/9.8) = 4.23 s <-- I believe this is the time for the entire drop? Then I subtracted 4.23-1.2 = 3.03 s <---- so thats the time the rock falls before the point at which i need to calculate the height. After that i get lost and can't seem to come up with a sensible answer. If someone could walk me through this I'd really appreciate it!