# Homework Help: Kinematics/free fall objects help.

1. Oct 9, 2011

### nando94

In my honors course we are covering kinematics concepts. There was this problem which stumbled me but then I figured out what I did wrong. I just want to make sure my concept was right. Here is the problem...

A diver springs upward with an intial speed of 1.8 m/s from a board that is 3 meters above
the surface of the pool (his displacement is y = -3m). What is the highest point he reaches above the water.

So this was my equation

vi = 1.8 m/s
vf = 0 m/s
a = -9.8 m/s2
x = ?

Solved the equation and got x = 3.16 or 3.2

So the part that kind of confused me in the begining was that I only had vi and vf. There had to be one more piece to solve the equation. Thats when I realized that gravity works even when the object has a positive velocity in the upward y direction. But then I started
doubting my self so Im kind of confused.

2. Oct 9, 2011

### Villyer

So are you confused about when to use -9.8 as the acceleration?

3. Oct 9, 2011

### nando94

Yeah basically. I was confused because he was going up and I kept thinking gravity in terms of falling down. So I wanted to make sure that gravity is the same when going up as well.