\large $$ m{{dV} \over {dt}} = \sum {F = F_g - F_b - F_d } $$
where,
\large $$ F_g - F_b = V_p (\rho _p - \rho _w )g $$ $$ F_d = {{C_D A_p \rho _p V^2 } \over 2} $$