The uniform 20-kg slender bar AC shown in Figure Q5 rotates in a vertical plane about the pin at B. The ideal spring AD has a spring constant k = 15 N/m and an un-deformed length Lo = 2 m. The bar, which is initially at rest in the position 0 = 0, is then released so that it rotates in a clockwise direction. Use the principle of conservation of energy to find the angular velocity of the bar when it reaches the horizontal position. 4 m D k = 15 N/m www L = 2 m A I 120-kg- I B C 2 m 3 m