A large boulder rests on a cliff 500 m above a small village in such a position that, if it should slide off, it would fall in the middle of the pond. The pond lies 80 m from the base of the cliff and has a width of 250 m. In the figure shown above, the angle ? is 20°. What is the initial speed of the boulder as it leaves the cliff? What is the final impact velocity of the boulder? vx ? vz ?