[填空题]
At a crime scene, the forensic investigatozn6o. 6ytw*h ufh(o dn m q,zv*.ih43inug7 0er l m 9ehi.a50kunotes that the 8.2-g lead bullet that was stopped in a doorframe apparently melted completeehm i0 u9.k5ally on impact. Assuming the bullet was fired at room temperature (20$^{\circ} C$ ), what does the investigator calculate as the minimum muzzle velocity of the gun? m/s