# Am I wrong or the teacher?

1. Feb 10, 2012

### -Physician

Okay, so our teacher gave us to define s=vt. Now i did it like that:
s=vt=(v_0+at)t=v_0 t+at2, but then, teacher said that's wrong, it should give you s=v_0 t+ \frac{1}{2} at2 Who is wrong me or teacher, If I am wrong, tell me where is my mistake, if the teacher is wrong let me know, thanks!

Last edited: Feb 11, 2012
2. Feb 10, 2012

### tskuzzy

I am assuming that this is a problem concerning the motion of a particle under uniform acceleration. In that case, the teacher is correct. The equation $s = vt$ is only correct for constant velocity. If velocity is not constant, then you must replace $v$ with the average velocity.

Under uniform acceleration, the average velocity is simply $\frac{v_0+v_f}{2}$.

3. Feb 10, 2012

### Staff: Mentor

You are wrong.

Are you familiar with calculus? Derivatives and integrals? That's one way to derive those equations.

4. Feb 10, 2012

### -Physician

So that would be $s=vt=\frac{v_0+v_f}{2}t=v_0 t + \frac{1}{2}$at2 or $s=vt=\frac{v_0+v_f}{2}t=v_f t - \frac{1}{2}$at2

Last edited: Feb 11, 2012
5. Feb 10, 2012

### tskuzzy

Yes that is correct.