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A metal cube of $20cm**20cm**20cm$ is sliding at a constant velocity of

$0\mathrm{.}9\frac{m}{s}$ down inside a sloping $U$ channel at $35$ to the horizontal as shown

in Fig. B Two $2mm$ vertical gaps and a $1mm$ bottom gap between the

cube and the channel interior surfaces are detailed in the Section X$-$X $($Fig$.$

B$\mathrm{.}6$a$($ii$)).$ The gaps are infilled with oil of dynamic viscosity $$ of $15N\frac{s}{m^2}$

Calculate the mass of the metal cube.

Fig. B