# Homework Help: Vector dynamics question starting from accelaration

1. Sep 27, 2010

1. The problem statement, all variables and given/known data
I took this right out of the text, it is not home work just me trying to get better.

The acceleration of a particle is defined by the relation a = -8 m/s^2
Knowing that x = 20 m when t= 4 m, and that x = 4 m when v = 16 m/s
(a) determine the time when velocity is zero and (b) the velocity and total distance travelled when t = 11 s

2. Relevant equations

3. The attempt at a solution
My attempt is I know velocity must be the integration of acceleration and displacement the integration of velocity. So I attempted to integrate -8dt 2 times. but when I do that I get x=-4t^2 which does not fit my given when t=4, x=20
Any help would be greatly appreciated, even just pointing me in the right direction

2. Sep 27, 2010

### fss

Looks like you need to take initial conditions into account. Remember that when you integrate you have a constant of integration as well, which you can determine if you have initial conditions (which you have).

3. Sep 28, 2010