A bullet is fired into a box & penetrates it . The penetration process melts it . Assuming that $\;25 \%\;$ of its K.E . goes in heating & the initial and final temperature are $\;27^{0}C\;$ & $\;327^{0}C\;$, the initial velocity is - (specific heat capacity = $\;100 Jkg^{-1}K^{-1}\;$ Latent heat of fusion = $\;2 \times 10^{4} Jkg^{-1}$)

Question

$(a)\;6.3 \times 10^{2}\;m/s\qquad(b)\;6.1 \times 10^{2}\;m/s\qquad(c)\;6.5\times 10^{2}\;m/s\qquad(d)\;6.6 \times 10^{2}\;m/s$