1. Sep 23, 2009

### kevinli

1. The problem statement, all variables and given/known data
Please explain these steps to me. My physics teacher went too fast :(

v=a*t
d=v*t
d=(a*t)*t
d=at2
Vaverage=Vf/2
=1/2Vf
d=1/2Vf*t
d=1/2at2

2. Relevant equations
v=a*t -> d=1/2at2

3. The attempt at a solution
N/A

2. Sep 23, 2009

### Fazza3_uae

Hi kevinli , welcome to PF ^^

first equation (v=a*t) is for Velocity = acceleration * time

in units = (m/s²)*(s) = (m/s) which is the SI unit for Velocity ^^

the second one (d=v*t) is for distance = velocity * time

in units = (m/s) * (s) = (m) which is also the SI unit for Distance

In this equation (d=(a*t)*t) he just substitued v with (a*t)

and he got this one (d=at2)

Here in this equation (Vaverage=Vf/2) i think he assumed Vi = 0
the initial velocity = 0 so the average Vf-Vi=Vf and divide by 2 ^^

He used the average velocity = (1/2)Vf in this equation d=v*t Instead of v

So he will get d= (1/2)Vf * t

and from first equation v=a*t

Or we can say Vf=a*t
we get

d=(1/2)at²

And finally i want to tell U that these equations will help U In free fall or projectiles
I hope i have explained what U want , & hope that u get it well now if it is what u want to know ^^

3. Sep 24, 2009

### Redbelly98

Staff Emeritus

Welcome to PF kevinli

What is v here? We talk about average, initial, and final velocity. Which velocity is it?