What is the Acceleration of a Small Body Moving on a Parabola?

[GregoryGr]

Homework Statement

a small body is moving in the plane xy with a constant (in size) velocity [ sorry for my english]. Find the acceleration for x=0 for the parabola $$y=ax^2$$

Homework Equations

The Attempt at a Solution

$$v^2= a_x^2 +a_y^2 \\ \vec{v}= a_x\vec{x}+ a_y*\vec{y}$$ and $$\vec{a}=d\vec{v}/dt$$

I'm kind of lost now, mainly because I'm new to differentiating vectors... Any help would be helpful...

 

[Panphobia]

Constant velocity means that acceleration is 0 or that the direction of velocity is changing, so is the velocity changing direction?

 

[haruspex]

The magnitude of the velocity is usually called the speed. If the speed is constant then any acceleration is orthogonal to the velocity. So what direction will the acceleration be in at x=0?
It remains to determine the magnitude of the acceleration. By differentiating the equations you have you should be able to determine $\ddot x^2+ \ddot y^2$ as a function of x and the speed.