A rifle of mass M is initially at rest. A bullet of mass m is fired from the rifle with a velocity of v relative to the ground. What is the expression that gives the velocity of the rifle relative to the ground after the bullet is fired?

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.