At a crime scene, the forensic investigator notes that the 6.2-g lead bullet that was stopped in a doorframe apparently melted completely on impact. The specific heat of lead is 130 J/kg⋅C∘, the heat of fusion is 25 kJ/kg, the melting point is 327∘C.
Assuming the bullet was shot at temperature 20 ∘C, what does the investigator calculate as the minimum muzzle velocity of the gun?