Question

A person is lifting a dumbbell weighing 25 kg. The person adopts a posture with the trunk inclined to a angle β and a tension (T) is exerted when the spine is stretched.

The forces acting on the column of the subject appear in the figure shown. The tension (T) can be located simplified to 2/3 of the length L (from the arm to the hip approximately) forming an angle α equal to 10º with its axis. Assume that the mass of trunk, head and upper limbs is equal to 55 kg, and that is located at the point of application of stress (center of gravity of these parts of the body coincides with that of T). A reaction is also generated in the person's coccyx due to the weight supported. (a) Determine the tension T and the components of the reaction in the coccyx joint Rx and Ry (vector R in the figure). (b) Determine the angle (γ) that the reaction R makes in the coccyx. Use the following values ​​of β: 45 °, 55 °, 65 ° and 75 °. What effect does the posture angle β have on the tension and reactions in the coccyx? Fill the Table.

45 10 65 75 2/3L pesa ex

Answer 1