I think the question here is about the initial velocity. If it is, then the working equation to be used is:
x = vt + 0.5at²
where
x is the distance
v is the velocity
t is the time
a is the acceleration
The acceleration due to gravity is 1.0g or 1.0(9.81 m/s²) = 9.81 m/s². There are approximately 3.154×10⁷ seconds in a year.
4.1×10¹⁶ m = v(2/3 yr * 3.154×10⁷ s/yr) + 0.5(9.81 m/s²)(2/3 yr * 3.154×10⁷ s/yr)²
Solving for v,
v = 1,846,769,088 m/s
