# One dimensional motion- object accelerating straight downwards

1. Jan 30, 2012

### texan14

One dimensional motion-- object accelerating straight downwards

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

A rocket, initially at rest, is fired at "t = 0" vertically down from a building of height "H". The rocket's acceleration, including the effects of gravity, is downwards with increasing magnitude given by a(t) = βt, where "β" is a known constant. When does it hit the ground and how fast is it going when it hits?

2. Relevant equations

xf = xi + vi*t + (1/2)*a*t2

3. The attempt at a solution

xf = (0) + vi*t + (1/2)*β*t2

I plugged everything into this equation, but it doesn't look right. I'm really confused. thanks in advance

2. Jan 30, 2012

### ehild

Re: One dimensional motion-- object accelerating straight downwards

Hi Texan14,

Is the acceleration constant? If not, why do you want to use the formula for constant acceleration?

Go back to the definition of acceleration.

ehild

3. Jan 30, 2012

### texan14

Re: One dimensional motion-- object accelerating straight downwards

I decided to integrate until I got the position function and solved for "t" and just plugged that into v(t). Thank you for your help, I don't know why I wanted to use that equation! haha

4. Jan 30, 2012

### ehild

Re: One dimensional motion-- object accelerating straight downwards

It does not hurt to read the the problem before plugging in everything to everywhere...:tongue2:

ehild