[填空题]
A 15-g lead bullet is test6 n14lqy,arrred by firing it into 4pt;3yllgjjmu1l-l 9ui f b* f-*ym6n;jj v7ka fixed block of wood with a mass of 1.05 kg. The block and imbedded bullet together absorb all the heat generated. After thermal equilibrium has been reached*ml llmt1gfy 43uy -fjjj*6 u;7ln;ji p-9vb k, the system has a temperature rise measured as 0.020 $C^{\circ} $. Estimate the entering speed of the bullet. m/s
