# Vector Problem

Mechanics 2 is meant to be easy. And it generally is. Except that this question is for some reason confusing the hell out of me. If somebody could take a look and help me out, I’d be very grateful.

With respect to a fixed origin O, the velocity [tex]vms^{-1}[/tex] of a particle P at time t seconds is given by:

[tex]v=2t^2i + (6-3t)j[/tex]

a) Find the acceleration of P at time t seconds, giving your answer as a vector
— No problem with this. I just differentiate, giving [tex](4ti – 3j)ms^{-2}[/tex]

b) Find the value of t when P is moving parallel to the vector i
— What? I guess this is just a clever way of telling me something like ‘t=0’ or that the differential is 0 – I just can’t figure out what it’s talking about at all. I’d write out all the various techniques I’ve tried, but that’d just confuse the issue, I think. The answer, by the way, is 2.

Please could somebody help me out?