physics..help PLEASE!
posted by kelsey on .
A 0.26 kg rock is thrown vertically upward from the top of a cliff that is 35 m high. When it hits the ground at the base of the cliff the rock has a speed of 28 m/s.
(a) Assuming that air resistance can be ignored, find the initial speed of the rock.
(b) Find the greatest height of the rock as measured from the base of the cliff.

(a) When air resistance can be ignored, the sum of potential and kinetic energy is constant. That means that V^2/2 + g h is constant, where h is the height measured from any reference plane. (The mass M cancels out). Use that fact to solve for the initial velocity Vo.
28^2/2 = Vo^2/2 + g*35
(b) At the greatest height, V = 0. use the same approach to solve for Hmax