Homework Help: Kinematics Problem

1. Feb 24, 2008

Below

1. The problem statement, all variables and given/known data

A student throws a stone vertically downward with an initial velocity of 5.0 m/s from the top of a 165 m building. How far does the stone travel during its 4th second of travel?

2. Relevant equations

d= vit + 1/2at2

3. The attempt at a solution

Vi = -5.0 m/s
t = 4.0 s
a = -9.81 m/s2
d = ?

I tried it in the kinematics equation d= vit + 1/2at2 and the answer is wrong.

2. Feb 24, 2008

Well, d=Vot+.5at^2
so d should be 98.4m. Did you get that?

3. Feb 24, 2008

Below

The answer given is 39 m.

4. Feb 24, 2008

Wait, I think it was the d for the 4th second, from 3-4s. Because the first second is 0-1s, second second is for 1-2s, etc.

So
Vf=vo+at
V@3=5+9.8*3 and V@4=5+9.8*4
(V@4)^2=(V@3)^2+2*9.8*d
Find d

Last edited: Feb 24, 2008
5. Feb 24, 2008

Below

d = displacement/distance.

6. Feb 24, 2008

Yes, i know.

7. Feb 24, 2008

Below

Is anyone going to help solve this problem please?

8. Feb 24, 2008

I just gave you the answer.

9. Feb 24, 2008