Which statement is true about wind energy? a) it is clean and non-polluting. b) it is only effective near water. c) it is costly and hard to produce. d) it is not as useful as fossil fuels.

The pressure proportional to the area a- inversely b- directly c- increase d-decrease

Convection currents are caused by differences in what two things?

Two identical stars with mass m orbit around their center of mass. each orbit is circular and has radius r, so that the two stars are always on opposite sides of the circle. (a) find the gravitational force of one star on the other. (b) find the orbital speed of each star and the period of the orbit. (c) how much energy would be required to separate the two stars to infinity?