A person bending forward to lift a load "with his back" (Fig. P8.15a) rather than with his knees" can be injured by large forces exerted on the muscles andvertebrae. The spine pivots mainly at the fifth lumbar vertebra, with the principal supporting force provided by the erector spinalis muscle in the back. To seethe magnitude of the forces involved, and to understand why back problems are common among humans, consider the model shown in Fig. PB.15b of a personbending forward to lift a Wo= 185 N object. The spine and upper body are represented as a uniform horizontal rod of weight W, 355 N, pivoted at the base ofthe 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 spineand this muscle is 12.0°. Find the tension in the back muscle and the compressional force in the spine.tension in the back muscleKNcompressional force in the spinelPivotBack muscleFigure PB.15(A)KN(b)12.0

Solution:-Given thatWo=185 NWb=355 N

A person bending forward to lift a load "with his back" (Fig. P8.15a) 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. To see the magnitude of the forces involved, and to understand why back problems are common among humans, consider the model shown in Fig. PS.15b of a person bending forward to lift a W, 185 N object. The spine and upper body are represented as a uniform horizontal rod of weight W-355 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 12.0°. Find the tension in the back muscle and the compressional force in the spine. tension in the back muscle KN compressional force in the spine Back muscle Pivot Figure PB.15 KN 12.0"

A person bending forward to lift a load "with his back" (Fig. P8.15a) 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. To see the magnitude of the forces involved, and to understand why back problems are common among humans, consider the model shown in Fig. PS.15b of a person bending forward to lift a W, 185 N object. The spine and upper body are represented as a uniform horizontal rod of weight W-355 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 12.0°. Find the tension in the back muscle and the compressional force in the spine. tension in the back muscle KN compressional force in the spine Back muscle Pivot Figure PB.15 KN 12.0"