Solve the all parts of given problem:
Problem: A 0.26-kg rock is thrown vertically upward from the top of a cliff that is 30m high. When it hits the ground at the base of the cliff, the rock has a speed of 29m/s.
Part I: Assuming that air resistance can be ignored, find the initial speed of the rock.
Part II: Find the greatest height of the rock as measured from the base of the cliff.
I need help to find the greatest height of the rock as measured from the base of the cliff.