Problems are listed in approximate order of difficulty. A single dot (•) indicates straigh...

Problems are listed in approximate order of difficulty. A single dot (•) indicates straightforward problems involving just one main concept and sometimes requiring no more than substitution of numbers in the appropriate formula. Two dots (••) identify problems that are slightly more challenging and usually involve more than one concept. Three dots (•••) indicate problems that are distinctly more challenging, either because they are intrinsically difficult or involve lengthy calculations. Needless to say, these distinctions are hard to draw and are only approximate.

••• (a) Consider an ideal gas at temperature T with molecules of mass m and number density (number per volume) n. Show that the number of molecules that strike a surface of area A in a time Δt is given roughly by . To simplify this calculation, consider a wall perpendicular to the x axis and make the radical assumption that the x components of the velocities of all molecules have the same magnitude; that is, assume that all molecules have the same |vx|, with half the molecules moving to the right and the other half moving to the left. (b) For oxygen at standard temperature and pressure (STP: T = 273 K, p = 1 atm = 1.01 × 105 N/m2), what is the average number of particles that strike a 1 cm2 surface in 1 s?