A $50-kg$ barrel $($IC $-2\mathrm{.}25kg*m2)$ starts from rest and is restrained by mass B $,$ which is supported by a cable wound around the barrel as shown Determine the mass of B so that the barrel has a velocity of $2\mathrm{.}4\frac{m}{s}$ at the bottom of the slope.

$(1$ pts$.)$