A small rock is thrown straight up with initial speed V0 from the edge of the roof of a building with height H. The rock travels upward and then downward to the ground at the base of the building. Let +y be upward, and neglect air resistance. (a) For the rock's motion from the roof to the ground, what is the vertical component Vav-y of its average velocity? Is this quantity positive or negative? Explain. (b) What does your expression for Vav-y give in the limit that H is zero? Explain. (c) Show that your result in part (a) agrees with Eq. (2.10).