determine the magnitude of the force exerted by the back muscles on the backbone (a measure of the strain in the back muscles). b. determine the magnitude of the force exerted by the pelvis on the backbone (a measure of the compression of the fluid-filled discs between the vertebrae in the lower back). c. how do these results explain why lifting in this way is unsafe? hint: how do the forces exerted by the cable and joint compare to the force exerted by the hanging 50 lb. object?