Hey guys I have attached a question I need help with.

I know that both posts are bases, hence ground level = 0. I was wondering if this means I assume that the z coordinate is related to the height above / below the ground.

Assuming this and going onto part a, t= root(5)/4 results in z coordinate 0

But when I go onto part B when trying to solving for an x coordinate 40, t is therefore equal to 10, giving you (40,12,z(t) ) But 10 is much greater then root(5)/4 which results in a negative z coordinate. This doesn't make sense to me, the ball can't be underground? Unless that is the answer to part C, stating that he doesn't score because the ball z(t) component is below 0.

I am surely missing something or misinterpreting something. Any assistant will be greatly appreciated.