Originally Posted by

**hollywood** Yes, Mr. Fantastic is right, you set the *magnitude* of v(t) to 57. So you have:

$\displaystyle v(t)=(2t+2)\ \mathbf{i}+2\sqrt{19}(t+1)^{1/2}\ \mathbf{j}+19\sqrt{6}\ \mathbf{k}$

If you let s=t+1 (just to make the algebra easier), and set the square of the magnitude of v(t) equal to 57 squared (setting the squares equal just to make the algebra easier), you get:

$\displaystyle 4s^2 + 76s + 2166 = 3249$

Which you can solve for s, and then t=s-1.

Post again in this thread if you're still having trouble.