Suppose two children push horizontally, but in exactly opposite directions, on a third child in a wagon. The first child exerts a force of 69.0 N, the second a force of 91.0 N, friction is 15.0 N, and the mass of the third child plus wagon is 23.0 kg.
What is the system of interest if the acceleration of the child in the wagon is to be calculated?

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.

Consider a double atwood machine constructed as follows: a mass 4m is suspended from a string that passes over a massless pulley on frictionless bearings. the other end of this string supports a second similar pulley, over which passes a second string supporting a mass of 3m at one end and m at the other. using two suitable generalized coordinates, set up the lagrangian and use the lagrange equations to find the acceleration of the mass 4m when the system is released. explain why the top pulley rotates even though it carries equal weights on each side.

Anika asks eva to roll a basketball and then a bowling ball to her. which requires more force to roll, and why?