[填空题]
At a crime scene, the forensic investigatoj dm7njlt43 bj3yy) (nr notdzr ;gvo* c,v)es that the 8.2-g lead bullet that was stopped in a doorframe z;vvod c gr,)*apparently melted completely 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