91Ó°ÊÓ

The weight \(W\) of an object above the earth varies inversely as the square of the distance \(\mathrm{d}\) from the center of the earth. If a man weighs 180 pounds on the surface of the earth, what would his weight be at an altitude of 1000 miles? Assume the radius of the earth to be 4000 miles.

The pressure of wind on a sail varies jointly as the area of the sail and the square of the wind's velocity. When the wind is 15 miles per hour, the pressure on a square foot is one pound. What is the velocity of the wind when the pressure on a square yard is 25 pounds?

A certain beam \(L \mathrm{ft}\). long has a rectangular cross section \(\mathrm{b}\) in. in horizontal width and \(\mathrm{d}\) in. in vertical depth. It is found that, when the beam Is supported at the ends, the deflection \(\mathrm{D}\) at the center varies directly as the fourth power of \(\mathrm{L}\), Inversely as \(b\), and inversely as the cube of d. If the length is decreased by 10 per cent but the width kept the same, by how much should the depth be changed in order that the same deflection D be obtained?