A gun is installed on the railway platform. The gun is rigidly attached to the platform. The mass of the platform and gun is M = 20 tons. The gun fires a shot at an angle α = 60° to the horizon in the direction of the path. What speed u1 does the platform with the gun acquire due to recoil if the mass of the projectile is m = 50 kg and it leaves the barrel with a speed u2 = 500 m/s?