Find the expressions for the unit vectors in cylindrical coordinate system, p 8,9,2. find the time-derivative of each. hints: unit vector rho is defined in (x, y) plane. remember that ã  . ñ is perpendicular to a the easiest way to find ñ is to express through ñ and add 90 degrees. 8

Hydroelectricity provides about 7 percent of the electricity generated in the united states. (a) explain how a hydroelectric power plant converts energy stored in water into electricity. (b) identify two factors that determine the amount of electricity that can be generated by an individual hydroelectricity power plant. (c) describe the two main types of land-based hydroelectric power plants. (d) describe two economic advantages and two environmental disadvantages of hydroelectricity.