Water exercise is often prescribed for patients with low back pain because it reduces the loads on the spine. If a person is standing immersed in water up to the base of the neck, the loads acting on the spine (more specifically, the 4th lumbar vertebra, LA in the figure below) are: Weight (W) of the body above the vertebra (head, neck, arms and trunk) acting downward at the center of mass 3 cm forward of the center of the L4 vertebra: 0.6*(body volume)*(density of body)*(gravitational acceleration, g). Buoyant force (B) from the water, acting upward at the center of mass 3 cm forward of the center of the L4 vertebra: 0.3*(body volume)*(density of water)* (gravitational acceleration, g). Force in the spine extensor muscle, acting at an angle of 20° from vertical, 2 cm behind the center of the L4 vertebra. Compressive force at the center of the L4 vertebra. In the figure below, the indicates the center of the L4 vertebra. Upper body B center of mass W 4 M C (a) Find the force in the muscle (M), when a 75 kg person is standing on land. (b) Find the compressive load on the vertebra (C), when a 75 kg person is standing on land. (c) How much does the compressive load on the vertebra (C) decrease, when the person is standing in the water!