Coulomb's law Coulomb's law in electrical theory states that the force F of attraction between two oppositely charged particles varies directly as the product of the mag- nitudes Q, and Q2 of the charges and inversely as the square of the distance d between the particles. (a) Find a formula for F in terms of Q, Q2. d, and a constant of variation k. (b) What is the effect of reducing the distance between the particles by a factor of one-fourth?

Power of a wind rotor The power P generated by a wind rotor is directly proportional to the product of the square of the area A swept out by the blades and the third power of the wind velocity v. Suppose the diameter of the circular area swept out by the blades is 10 feet, and P = 3000 watts when v = 20 mi/hr. Find the power generated when the wind velocity is 30 mi/hr.