A lamina occupies the region inside the circle x2 + y2 = 10y but outside the circle x2 + y2 = 25. Find the center of mass if the density at any point is inversely proportional to its distance from the origin.

22. the top of a cliff is located a distance h above the ground. at a distance h/2 there is a branch that juts out from the side of the cliff, and on this branch a bird's nest is located. two children throw stones at the nest with the same initial speed, one stone straight downward from the top of the cliff and the other stone straight upward from the ground. in the absence of air resistance, which stone hits the nest in the least amount of time?