A lead bullet penetrates into a solid object and melts. Assuming that 40% of its kinetic energy is used to heat it, the initial speed of bullet is:
(Given, initial temperature of the bullet $=127^{\circ} \mathrm{C}$, Melting point of the bullet $=327^{\circ} \mathrm{C}$, Latent heat of fusion of lead $=2.5 \times 10^4 \mathrm{~J} \mathrm{Kg}^{-1}$, Specific heat capacity of lead $=125 \mathrm{~J} / \mathrm{kg} \mathrm{K}^{\mathrm{K}}$ )