# Rectilinear Motion

1. Aug 3, 2011

### BloodyFrozen

I can't remember how to derive this equation...

x(fluxion)
a=acceleration

x=a

From that, how do we get->

at^2+v+h

I think it had to do with integration, but I can't seem to get it to match the above.

2. Aug 4, 2011

### tiny-tim

Hi BloodyFrozen!

(try using the X2 icon just above the Reply box )

I don't understand what you mean by "fluxion" or "x=a"

Try starting with dv/dt = a (and dx/dt = v).

3. Aug 4, 2011

### BloodyFrozen

Anyways, I think I got it...

dv/dt = a
v(t)=at+C1
v0=C1

v(t)=at+v0
x(t)=at2+v0t+C2
x0=C2

Therefore,

x(t)=at2+v0t+x0

Since x0 is the position at t=0, he can just replace it as the original height.

x(t)=at2+v0t+h0

Correct?:rofl:

4. Aug 4, 2011

### tiny-tim

erm

what happened to the 1/2 ?

5. Aug 4, 2011

### BloodyFrozen

1/2at2...

In one of the calculus review books, it says it's -1/2at2... Why is it that?

6. Aug 4, 2011

### tiny-tim

i'll guess it's talking about something being thrown up

so if v0 is positive, then the acceleration is negative