Answer to Question #64201 in Other Physics for Rawan
When the trunk is bent forward, the spine pivots mainly on the fifth lumbar vertebra . The figure shows the forces involved when the trunk is bent at 60◦ from the vertical with the arms hanging freely. The lever model representing the situation is given. The pivot point A is the fifth lumbar vertebra. The lever arm AB represents the back. The weight of the trunk W1 is uniformly distributed along the back; its effect can be represented by a weight suspended in the middle. The weight of the head and arms is represented by W2 suspended at the end of the lever arm. The erector spinalis muscle, shown as the connection D-C attached at a point two-thirds up the spine, maintains the position of the back. If for a 70-kg man the angle between the spine and this muscle is 12◦ , the length of his back is 48 cm, and W1 and W2 are 320N and 160N , respectively, calculate the tension T and the compression force on the fifth lumbar.