Posted by **kelsey** on Wednesday, October 8, 2008 at 12:42am.

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.

- physics..help PLEASE! -
**drwls**, Wednesday, October 8, 2008 at 1:52am
(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

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