Steven buys a pair of scissors instead of getting a haircut. he belives the scissors will last for a long time, while the haircut will only last a few weeks. in this case, scissors is a good, while the haircut is a service. why is the haircut considered a service here?

Will you chech and finish these for me, because i am stumped with them.

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.

If a balloon is taken outside on a very cold day, what will occur?