(Roiaiionai Equilibrium) Jane is bending forwards, keeping her back horizontal as shown schemati- cally in the gure below, with Jane's hips at point A and her shoulders at point D. It is reasonable to approximate Jane's spine as a rigid bar, with the weight of her upper body applying a weight force IV = 420N at point B and her back muscles applying a tension force T at point C, at an angle 9 above the horizontal. The distance between points A and D is L, between points A and B is 0.6L and between points A and C is 0.7L. Jane's back muscles apply enough tension T to maintain her back in a horizontal position. Her legs apply a reaction force R through her hips to maintain equilibrium. If she is trying to lift a load we approximate that as a vertical force L applied at point D. A/R Y;\\ o B c w L Notes: 1. In order to remain stationary the spine must be in mechanical equilibrium, i.e. in translational and rotational equilibrium. 2. The torque produced by a force F about a pivot is equal to the magnitude of F multiplied by the perpendicular distance from the pivot to the imaginary line along which the force acts. For example, in the above gure, the torque 7' produced by the weight I'V about point A is T 2 0.6L >