You are standing at the top of a cliff that has a stair step configuration. There is a vertical drop of 7 m at your feet, then a horizontal shelf of 8 m, then another drop of 3 m to the bottom of the canyon, which has a horizontal floor. You kick a rock, giving it an initial horizontal velocity that barely clears the 8 m shelf below.

Question

You are standing at the top of a cliff that has a stair step configuration. There is a vertical drop of 7 m at your feet, then a horizontal shelf of 8 m, then another drop of 3 m to the bottom of the canyon, which has a horizontal floor. You kick a rock, giving it an initial horizontal velocity that barely clears the 8 m shelf below.
What initial horizontal velocity v will be required to barely clear the edge of the shelf below you? The acceleration of gravity is 9.8 m/s2 . Consider air friction to be negligible.
Answer in units of m/s

Damon · Accepted Answer

I use u for horizontal and v for vertical first do a 7 m vertical fall v = g t h = (1/2) v t^2 7 = 4.9 t^2 t = 1.2 sec so it must go horizontal 8 m in 1.2 s so u = 8/1.2 = 6.7 m/s horizontal