A worker needs to lift a box with a mass of $20$ kilograms from the ground and place it on a shelf thatis $0\mathrm{.}8$ meters high. The worker uses a stooped lifting posture, meaning he keeps his legs straight andbends his back $($stooping lift$).$ The total mass of the worker$$s upper body $($head$,$ arms, and torso$)$ is $40$kilograms. The horizontal distance from the L$5/$S$1$ intervertebral disc $($located at the base of the spine$)$to the center of mass of the upper body is $30$ centimeters, and to the center of mass of the box is $50$centimeters.According to the NIOSH $($National Institute for Occupational Safety and Health$)$ guidelines, themaximum acceptable compressive force on the L$5/$S$1$ disc is $3400$ Newtons. The erector spinae muscles,which provide the lifting force, have an effective moment arm of $6$ centimeters at the L$5/$S$1$ disc.