Question 465947
Because the height as a function of time is a quadratic, there can be two answers. The graph of the quadratic and the height h = 15 m intersect at two places, as shown:


{{{graph(400,400,-5,20,-5,20,20x-5x^2, 15)}}}


Note that the height vs. time graph is quadratic because acceleration due to gravity is constant (ignoring air resistance) and from this we can show that the position vs. time graph is quadratic using introductory physics and calculus.