Answer Happy

A person bending forward to lift a load "with his back" (Figure
a) rather than "with his knees" can be injured by large forces
exerted on the muscles and vertebrae. The spine pivots mainly at
the fifth lumbar vertebra, with the principal supporting force
provided by the erector spinalis muscle in the back. To see the
magnitude of the forces involved, and to understand why back
problems are common among humans, consider the model shown in
Figure b, of a person bending forward to lift
a Wo = 220–N object. The
spine and upper body are represented as a uniform horizontal rod of
weight Wb = 410 N pivoted
at the base of the spine. The erector spinalis muscle, attached at
a point two-thirds of the way up the spine, maintains the position
of the back. The angle between the spine and this muscle
is 12.0°.
In figure (a), a man bends his back forward to lift a set of
weights. The hips are labeled as the pivot and the back muscle is
also labeled to the right of the pivot. In figure (b), a horizontal
rod is shown. There are two points on the rod. One of the points is
on the left end of the rod and an arrow
labeled Rx extends rightward from the
point while an arrow
labeled Ry extends upward from the
point. The second point is slightly to the right of the center of
the rod. An arrow labeled
vector T originates from here and points
up and to the left making and angle 12.0° with the horizontal.
An arrow labeled Wb originates from
the center of the rod and points down, it is shorter than
vector T. An arrow
labeled Wo originates from the right
end of the rob and points down. It is shorter
than Wb.
(a) Find the tension in the back muscle.
kN

(b) Find the compressional force in the spine. (Enter the
magnitude.)
kN
DETAILS MY NOTES ASK YOUR TEACHER 7. 1-14 Points) A person bending forward to in a sad with his back (gure a) rather than with his knees can be injured by large forces exerted on the muscles and vertebrae. The spine pivots mainty at the fifth -220-N object. The spine and upper body are represented as a uniform horizontal rod of - tumber vertebra, with the principal supporting force provided by the erector spinals muscle in the back. To see the magnitude of the forces involved, and to understand why back problems are person bending forward to onun among humana, consider the model shown in Figure , c point two-thirds of the way up the spine, maintains the position of the back. The angle between the wght w-410 N pvoted at the base of the spine. The erector spine and the muscle 12.0 Back che Y 120 Pun W₂ () Find the tension in the back musos AN (0) Find the compressional force in the spine Enter the magnitude) AN Need Help?