Another one that's been troubling me

[Cowtipper]

Homework Statement

A student is riding on a flatcar of a train traveling along a straight horizontal track at a constant speed of 10.0 m/s. The student throws a ball along a path that she judges to make an initial angle of 60 degrees with the horizontal and to be in line with the track. The student's professor, who is standing on the ground nearby, observes the ball to rise vertically. How high does the ball rise?

Homework Equations

These are what I'm pretty sure are necessary:

dyMax = maximum height of y
Vi = initial velocity
g = gravity

dyMax = (Vi^2) / (2g)

The Attempt at a Solution

Vx = 10cos60 = 5 m/s
Vy = 10sin60 = 8.66 m/s

gx = 0
gy = 9.81

dyMax = (8.66^2) / (2 * 9.81)

I got 3.822 meters as the answer, although I'm pretty sure that's wrong. Any ideas? Thanks.

 

[catkin]

Why do you think it's wrong? And why do you list Vx and gx?