Which statement is true? a) geothermal power plants use the renewable resource of heat from within the earth to generate electricity. b) hydroelectric energy uses the energy from the sun, which is a renewable resource. c) oil is a nonrenewable resource that is hardly ever used, so there is not a concern of depleting the earth's supply. d) solar energy is a nonrenewable resource that is used by many countries all over the world.

Amerry-go-round of radius r, shown in the figure, is rotating at constant angular speed. the friction in its bearings is so small that it can be ignored. a sandbag of mass m is dropped onto the merry-go-round, at a position designated by r. the sandbag does not slip or roll upon contact with the merry-go-round. how would you rank the following different combinations of m and r on the basis of the angular speed of the merry-go-round after the sandbag "sticks" to the merry-go-round from largest to smallest. a) m = 10kg, r = 0.25r b) m = 20kg, r = 0.25r c) m = 10kg, r = 0.50r d) m = 10kg, r = 1.0r e) m = 15kg, r = 0.75r f) m = 40kg, r = 0.25r