5. A stone is thrown horizontally from the top of a 80.50m cliff. The stone lands at a distance of 10.00 m from the edge of the cliff. What is the initial horizontal velocity of the stone?
Im not good with projectiles.

There is no force on it in the horizontal direction ( we neglect air resistance) so the horz vel does not change.
Since it was thrown horizontally, its initial velocity in the vertical dierection is zero. Use s = ut + 0.5gt^2 withu, the initial vel = 0.
From this, find t.
The horizontal distance is simply Vhorz x t. So

Vhorz x t = 10.00 .Solve for Vhorz.

In projectiles always resolve the velocity into its vertical and horizontal components. Then treat them independently remembering that the horz vel doesn't change in problems where air resistance is neglected.
It is quite simple actually one you get the hang of it.