Asolar heated house loses about 5.4 × 107 cal through its outer surfaces on a typical 24-h winter day.

what mass of storage rock is needed to provide this amount of heat if it is brought up to initial temperature of 62°c by the solar collectors and the house is maintained at 20°c? (specific heat of rock is 0.21 cal/g⋅°c.)

a. 163 kg
b. 1 230 kg
c. 6 100 kg
d. 12 700 kg

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.