- #1

- 72

- 0

**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 that's 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!