"an empty cylindrical barrel is open at one end and rolls without slipping straight down a hill. the barrel has a mass of 19.0 kg,19.0 kg, a radius of 0.260 m,0.260 m, and a length of 0.650 m.0.650 m. the mass of the end of the barrel equals a fifth of the mass of its side, and the thickness of the barrel is negligible. the acceleration due to gravity is