# Very simple question about kinematics

1. Jul 12, 2012

### Bengo

I feel like I'm missing a large concept of the kinematics equation. Up until today, I have only used them for HALF of a trajectory (initial velocity and final velocity of 0 at the apex). But can you use them for an ENTIRE trajectory? So say something is fired from the ground and lands on the ground at the same level. If you plug in the initial velocity and use the entire flight time, will you get the same final velocity from these equations?? I'm so confused. Please help me get this sorted out before I take the MCAT.

2. Jul 12, 2012

### Staff: Mentor

Sure. Why not give it a shot? (The same speed, at least.)

3. Jul 12, 2012

### genericusrnme

Which kinematics equations are you using?
(most of the basic kinematics equations you get will work fine for a trajectory however long you want though)

4. Jul 12, 2012

### CWatters

Try it. What happens if you apply this equation to say a bullet fired straight up?

V2=U2+2as

Remember that if up is +ve then a is -ve.

What happens to s after the apex?

5. Jul 12, 2012

### Bengo

genericusrnme, I was just talking about those formulas for a projectile motion from a physics 1 class.

But I see that it works now, the trajectory is symmetric so I guess I just have to be careful about the signs?

Thank you!