A block of mass m starts from position 1 and moves up a frictionless inclined plane with an initial speed v. At some later time the block has moved down the plane and at position 2 has a speed u. If a and b are the heights above the bottom of the plane, the magnitude of u can be determined from
A) u^{2} = v^{2} - 2g(a - b)
B) u^{2} = v^{2} + 2g(a + b)
C) u^{2} = v^{2} + 2g(a - b)
D) u^{2} = v^{2} + 2g(b - a)
E) u^{2} = v^{2} + g(a - b)