# Homework Help: Physics Kinetic Energy Question

1. Sep 18, 2009

### Ion1776

You are about shoot two identical cannonballs straight up into the air. The first cannonball has 2.0 times as much initial velocity as the second. How many times higher will the first cannonball go compared to the second?

How do you do this

2. Sep 18, 2009

### Feldoh

Total energy = Kinetic + Potential in this scenario, right? Also note that the energy is conserved (well, assuming no air resistance)

As each ball travels higher into the air the potential becomes larger, which means the kinetic energy decreases until all the energy is potential. This is where each ball will stop.

Does this help?

3. Sep 18, 2009

### Ion1776

So what formula should I used, how should i plug the numbers in

4. Sep 18, 2009

### physicsface

I actually don't think you need kinetic energy for this... Try using kinematics equations.

5. Sep 18, 2009

### Ion1776

How about helping me out, and showing me how to do this.

I know my equations, I dont know what to use, plus I need to understand the concept....

6. Sep 18, 2009

### physicsface

Well, since they're both shot straight up, the only acceleration you need to worry about is gravity. Find an equation with only initial and final velocity, acceleration, and displacement. Set the equations equal to each other. Solve for final position.

Sorry, there's really not too much more I can say without giving you the work, and the point is just to point you in the right direction.