Figure 1 shows a simplified diagram of the forces involved in lifting a heavy object of mass L of 30 kg with the arms.Assuming that the centre of gravity of the trunk is two-thirds of the way up the spine between the lumbosacral joints and the arms, determine:
a) The Compressive force, S, on the lumbosacral disc.
b) The angle (θ), that the force, S, acts to the column.
c) If the force required to rupture the disc is 15,000 N determine the mass (in kg) that can be lifted by the arms without causing damage to the disc.(Assume the total body weight is 700 N).
（Figure 1 The diagram shows a simplified view of forces involved in lifting an object. The effort (E) is provided by the extensor muscle attached to the pelvis at approximately 10°to the vertebral column. There is a compressive force (S) on the lumbosacral disc and the weight of the upper body (head, arms and trunk) is represented by Wb.）