# Homework Help: What am I doing wrong in this basic Projectile Motion Problem?

1. Feb 9, 2012

### volleyballkay

What am I doing wrong in this basic Projectile Motion Problem??

What I did in was use Delta X = Vxi + axt^2 & Delta Y= Vxi + ayt^2

then I plugged in the information but acceleration for x was 0m/s^2 and acceleration for y was -9.80m/s^2.

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Last edited: Feb 9, 2012
2. Feb 9, 2012

### cepheid

Staff Emeritus
Re: What am I doing wrong in this basic Projectile Motion Problem??

Welcome to PF!

I don't know whether this is the only thing you are doing wrong, but it does seem like there are a few errors with your equations. It should be:

Δx = vxit + (1/2)axt2

The parts you were missing are shown in bold.

Last edited: Feb 10, 2012
3. Feb 9, 2012

### ehild

Re: What am I doing wrong in this basic Projectile Motion Problem??

The stone was thrown vertically upward. If Δx means horizontal displacement, the initial horizontal velocity is zero, the horizontal acceleration is zero, is Δx different from zero?
You need to work only with ΔY=Vyit + ay/2* t^2. ay = -9.8 m/s^2, that is correct. What is the initial velocity? What is ΔY when the stone strikes the ground?

ehild

4. Feb 10, 2012

### cepheid

Staff Emeritus

Yeah I did. That was a very unfortunate typo.

5. Feb 10, 2012

### cepheid

Staff Emeritus
Re: What am I doing wrong in this basic Projectile Motion Problem??

Edited