A person bending forward to lift a load "with this back" rather than "with his knees" can be injured by large forces exerted on the muscles and vertebrae. The spine pivots mainly at the fifth lumbar vertebra, with the principal supporting force provided by the erector spinalis muscle in the back. Consider the model of a person bending forward to lift a 200-N object as shown in the figure. The spine and the upper body are represented as a uniform horizontal rod of weight 350 N, pivoted at the base of the spine. The erector spinalis muscle, attached at a point two-thirds of the way up the spine, maintains the position of the back. The angle between the spine and this muscle is 12.0o. Find (a) the tension in the back muscle and (b) the compressional force in the spine.
