Answer
This means that the slope needs to be 30 degrees below the horizontal.
Work Step by Step
We first find the change in time:
$55=28cos(9.5)t \\ t = 1.99 \ s$
We now find the change in y:
$\Delta y = -28sin(9.5)(1.99)-\frac{1}{2}g(1.99)^2=-28.65 \ m$
Thus, we find the angle they will be at:
$\theta=tan^{-1}(\frac{28.65}{55})=27^{\circ}$
This means that the slope needs to be 30 degrees below the horizontal.
