The position function of a particle is given by r(t)=⟨−1t2,−4t,t2+4t⟩.
At what time is the speed minimum?

Question

The position function of a particle is given by r(t)=⟨−1t2,−4t,t2+4t⟩. 
At what time is the speed minimum?

anonymous · Answer

I got about as far as finding the magnitude of the velocity vector which is sqrt(8t^2+16t+32) but not sure where to go from here.

anonymous · Answer

set d/dt (speed) = 0. in other words, a(t) = 0

anonymous · Answer

yeah, so it should be sqrt(32).  i tried that and it didn't work.

anonymous · Answer

oh, wait, i have to integrate the whole sqrt thing again and set that equal to 0?  grr....

anonymous · Answer

not integrate. Differentiate. and yeah you do that again

anonymous · Answer

ok thanks.  lemme see if that works

anonymous · Answer

it worked.  thanks @sourwing !

anonymous · Answer

no prob