# Homework Help: Physics 1-D kinematics

1. Sep 17, 2009

### sucksatphysic

1. The problem statement, all variables and given/known data
Sitting on a tree branch 10 m above ground. Drop chestnut 1. When chestnut 1 has fallen 2.5 m, I throw a second chestnut straight down.

What is the initial speed of chestnut 2, if they are to both reach the ground at the second time
??

2. Relevant equations

X=Xo + Vo t + 1/2 at2

a=g
For chestnut 1 v=0
X=1/2gt^2
3. The attempt at a solution

So i got the first chestnuts time, which was
t=(2x/g)^1/2 = 1.4 seconds.

The problem i'm having now is what to do next. Am I supposed to find chestnut 1's time at 2.5? I'm so confused... thanks for helping =)

2. Sep 17, 2009

Instead of finding the time 't' it takes Chestnut 1 to reach the ground from start to finish, find out how long it takes from the time it has fallen 2.5m (i.e. x=7.5m)until it hits the ground. Call this time 't1'

Then, Chestnut 2's velocity must satisfy the condition that it causes the nut to reach the ground in that same amount of time = 't1'.

3. Sep 17, 2009

### rl.bhat

How much time chestnut takes to fall through 2.5 m?
Total time - the above time = the time taken by chestnut 2 to reach the ground.

4. Sep 17, 2009

### sucksatphysic

ok, so i did that, and i got 1.2365 seconds.

so that, and now should i use that time in the X=Xo + Vo t + 1/2 at^2 ?

what should I put for X and Xo?

Sorry, i've just been stuck on this question forever lol.