4. The bar has a mass of 10 kg and is subjected to a couple moment of M=50 N·m and

4. The bar has a mass of 10 kg and is subjected to a couple moment of M=50 N·m and a force of P=80 N, which is always applied perpendicular to the end of the bar. The stiffness of spring is k=30 N/m and its free length is 0.5 m. The spring remains in the vertical position due to the roller guide at B. Determine the total work done by all the force acting on the bar when it has rotated downward from (=0( to 90 (. (15 points)