1. The problem statement, all variables and given/known data A person standing at the top of a hemispherical rock of radius R kicks a ball (initially at rest) to give it a horizontal velocity vi. a. What must be the rock’s minimum speed if the ball is never to hit the rock after it is kicked? b. With this initial speed, how far from the base of the rock does the ball hit the ground? 2. Relevant equations Projectile Motion 3. The attempt at a solution I tried my way a couple times but the answer I get is wrong. Ok I tried to find the function of the curve of the rock. Setting y=0 at the top of the rock, I get y=-(gt²)/2. And vt=R. Solving for t when y=-R t=√(2r/g) and v=(√Rg)/2. Is this not vmin? I even checked it by putting vmin back into the y as function of x. Then I put something bigger back into that same function and y is greater for vmin. This means that the ball is always higher than the rock if kicked greater than (√Rg)/2. The answer key says vmin=(√Rg). What did I do wrong?