A small rock is released from rest at the edge of a cliff that is 25m above the base of a waterfall. A vertical one-dimensional coordinate axis is chosen with its origin at the cliff edge and the positive direction defined as upward.
(1) Determine the signed displacement of the rock from the moment of release until it strikes the water at the base of the waterfall. Include the correct algebraic sign and appropriate units.
(2) State the algebraic sign of the rock’s velocity just before impact, and explain how you determined this sign without calculating the speed.
(3) Suppose instead that a student chooses the downward direction to be positive while keeping the origin at the cliff edge. For this alternative coordinate system, give the signed value of the rock’s displacement upon impact and state the sign of its velocity at that instant. Explain how and why each sign has changed or remained the same.