The largest-caliber antiaircraft gun operated by the German air force during World War II was the 12.8 cm Flak 40. Suppose this weapon fired a 22.8 kg shell with a muzzle speed of 770 m/s. What propulsive force was necessary to attain the muzzle speed within the 6.00 m barrel? (Assume the shell moves horizontally with constant acceleration and neglect friction.)