No need for physics calculations except from the equation given in the description. Also, I don't understand why you talk about flight angle, it's not question about that, the direction is always vertical and one only needs to take into account the initial speed.

Try adding a continue; after your k = k - 1;

Clever and original but definetely not a seven kyu!

Not sure if I am dumb or if this Kata is. Maybe it's not a legit 6 and I am just missing something subtle.

I did end up liking this quite a bit because it made me do some math research. I think the initial equation you are given could be different. Instead of thinking about it like a programming problem, I thought of it as a physics problem which helped. That eliminated the use of the while or for loop. As a small hint: Find total flight time based of velocity and flight angle.

Remember, since the object being thrown does not exceed terminal velocity (specifically initial velocity), flight time should be symmetrical.

Have you tried foreach loops?