$7\mathrm{.}1$ A hundred particles of equal size and density are released simultaneously and allowed to settle in still air for $5$min. Because of Brownian motion along the vertical axis, some particles will progress farther than others. If the particles are $0\mathrm{.}6$m spheres of standard density, what are the mean and standard deviation of their displacements from origin after $5$min? ANSWER: $4\mathrm{.}1$mm$,0\mathrm{.}17$ mm$.$