After a comb is rubbed on a wool sweater, it is able to pick up small pieces of paper. why does the comb lose that ability after a few minutes

The ratio of lift to drag l/d for a wing or airfoil is an important aerodynamic parameter, indeed, it is a direct measure of the aerodynamic efficiency of the wing. if a wing is pitched through a range of angle of attack, l/d first increases, then goes through a maximum, and then decreases. consider an infinite wing with an naca 2412 airfoil. estimate the maximum value of l/d. assume that the reynolds number is 9x10^6.

A15.75-g piece of iron absorbs 1086.75 joules of heat energy, and its temperature changes from 25°c to 175°c. what is the specific heat capacity of iron?

Which system of units is used by only a small number of countries in the world, including the u. s.