Constant acceleration dotted with constant velocity?

So I have been told at time t=0 a particle leaves the origin, with initial velocity V, and is subject to a steady acceleration A.

Part of the question asks me to find X(displacement) dot V hat (V hat being the unit vector in direction on V)

I have already found an expression for X previously. Anyway I have written the answer out in terms of A and V and t, and part of the expression contains: A dot V. Now for my answer to match that of the mark scheme, A dot V has to be 0...I know a constant acceleration and constant speed implies that velocity and acceleration are orthogonal (and hence have a dot product of 0), but I'm not sure how this applies here since V is a constant vector. Is there some reason why A and V dotted are zero, or have I gone wrong and by chance my answer matches the markscheme when I set them equal to 0?

Any help is appreciated, thanks!

Is there any chance you can upload or link us to the original question and mark scheme?

It's a bit difficult to comment just on the basis of what you've posted

Essentially I have a constant acceleration A. An initial velocity V. Why is V dot A = 0

There is no reason for V.A to equal zero based on what you have posted.

Which is why you're being asked to post the entire question.

at t = 0, particle leaves origin, with initial velocity V and is subjected to constant acceleration A. The angle between them is theta, where theta is greater than 0 but less than or equal to pi.

By finding expressions for v(t) AND x(t), evaluate x(t) dot V hat (unit vector in direction on V).

That's the first part. I think this may be where I'm going wrong