Problem: A rock is thrown directly upward from the edge of a flat roof of a building that is 56.3 meters tall. The rock misses the building on its way down, and is observed to strike the ground 4.00 seconds after being thrown. Take the acceleration due to gravity to have magnitude 9.80 m/s2 and neglect any effects of air resistance.
Part I: With what speed was the rock thrown?
I want help to calculate With what speed was the rock thrown.