# Kinematics Equations (2 Problems!)

1. Sep 17, 2008

### Johnny_07

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

In solving a kinematic equation for x, which has a negative acceleration, is x necessarily negative?

A classmate states that a negative acceleration always means that a moving object decelerating. Is this statement true? Explain.

2. Relevant equations

3. The attempt at a solution

2. Sep 17, 2008

### solarwind

No, depends on reference. You can say gravity has a negative acceleration in the y prime, but a falling object is accelerating. The correct term is negative acceleration, not decelerating.

Note: I could be wrong.

Last edited: Sep 17, 2008
3. Sep 17, 2008

### Johnny_07

Thanks for the help, but it's two problems in my book, and those are the exact words. So I don't know.

4. Sep 17, 2008

### solarwind

For your first question, what is x? Is it displacement, velocity or what?

5. Sep 17, 2008

### Johnny_07

I have no idea. I believe it's displacement, if I'm not mistaken. My teacher and the textbook is really vague and not clear at all :(

6. Sep 17, 2008

### solarwind

Haha! I know how that is...

The answer is NO. This is because x could have a positive displacement and could also have a negative acceleration (slowing down) at the same time. Example, you roll a ball on the floor. It moves away from you (positive displacement) but is also slowing down (negative acceleration).

Again, I could be wrong, I'm only in last year of high school physics.

7. Sep 17, 2008

### Johnny_07

Alright, I'll take that into consideration.
Thanks alot again! :) Really helped!