$15$ kg of particles of particle density $2000$ kg$/$m$3$ are fluidized in a vessel of cross$-$

sectional area $0\mathrm{.}03$m$2$ by a fluid of density $900$ kg$/$m$3.$

$($a$)$ What is the frictional pressure drop across the bed if the bed height is $0\mathrm{.}6$ m$,$ what

is the bed voidage?