Ok, so there are two stones. One is dropped (not thrown) off a building. 2 seconds later a rock is thrown at 30 m/s. The rocks hit the ground at the same time. Here's what I have so far:(adsbygoogle = window.adsbygoogle || []).push({});

R1:

v0 = 0 m/s

T = unknown

x = o m

x0 = unknown

a = 9.8 m/s^2

R2:

v0 = 30 m/s

T = Time of R1 - 2 s

x = o m

x0 = unknown

a = 30 m/s @ 9.80 m/s^2

I know that these two equations must equal eachother:

(.5)(9.80 m/s^2)(T)^s = (30m/s)(T-2) + (.5)(9.80m/s^2)(T-2)^2

However, I have expanded this a million times and for some reason I can't get things to click. I mean, I could do guess and check but there has got to be an easier way...

The question asks how long it took the first stone to reach the gound, how high the building is, and what speeds the stones are at before they hit the ground.

Since they ask for the time first, I thought I would have to use the 2nd kinematic equation. But then I realized that I dont know what the initial height was. I feel stuck because I have these two variables the initial height and time. What do I use to find these one at a time? Lol, I'm stuck.

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Two Stones Falling

**Physics Forums | Science Articles, Homework Help, Discussion**