Quick questions on Projectile motion: WACE Year 12 Physics Unit 3

For a launch speed $u$ at angle $\theta$ above the horizontal,

The cliff or table launch is where most marks are lost, so treat it carefully. Choose up as positive and place the origin at the launch point. The vertical displacement at landing is then negative (the ground is below the launch), which is the sign that makes the quadratic $y=u_y t-\tfrac{1}{2}gt^2$ produce a sensible positive time. Solving that quadratic with the formula gives two roots; discard the negative one as unphysical.