# Thread: find the velocity vector for an object

1. ## find the velocity vector for an object

find the velocity vector for an object having

$\vec a(t) = e^t \hat{j} -32 \hat{k}$

if

$v(0) = 3 \hat{i} - 2 \hat{j} + \hat{k}$

Im not sure how to proceed. Would i integrate? How to handle the v(0) has me confused!

$v(t) = \int e^t \hat{j} -32 \hat{k}\ dt$

$v(t) = e^t j -32t k + c$

Im not sure if i am doing this correctly?

2. ## Re: find the velocity vector for an object

Originally Posted by icelated
Im not sure if i am doing this correctly?
Yes. The initial velocity, $\mathbf v(0),$ is an initial condition. Use it to determine the constant of integration.

$\mathbf v(t) = e^t\mathbf j-32t\mathbf k + \mathbf C$

So

$\mathbf v(0) = 3\mathbf i - 2\mathbf j + \mathbf k$

$\Rightarrow e^0\mathbf j-32\cdot0\mathbf k + \mathbf C = 3\mathbf i - 2\mathbf j + \mathbf k$

$\Rightarrow\mathbf C = 3\mathbf i - 3\mathbf j + \mathbf k$

3. ## Re: find the velocity vector for an object

Would i then integrate again?

Here is the final answer, but i cant seem to get to it

$v(t) = 3i +(e^t - 3)j +( -32t +1)k$

4. ## Re: find the velocity vector for an object

Originally Posted by icelated
Would i then integrate again?
Why would you?

Originally Posted by icelated
Here is the final answer, but i cant seem to get to it

$v(t) = 3i +(e^t - 3)j +( -32t +1)k$
Just substitute what you (I) found for $\mathbf C$ back into the equation for $\mathbf v(t).$ That's it.

5. ## Re: find the velocity vector for an object

I can see that now! Thank you..
Problems like this in the book integrate. ybe if v(0) = 0?