258 TOPIC 8 | Rotat 23. BIO A person bending forward to lift a load "with his back" eg (Fig. P8.23a) 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 P8.23b of a person bend- ing forward to lift a 200.-N object. The spine and upper body are represented as a uniform horizontal rod of weight 350. N, pivoted at the base of the spine. The erector spinalis muscle, attached at a point two-thirds of the way up tains the position of the back. The angle between the spine and this muscle is 12.0°. Find (a) the tension in the back mus cle and (b) the compressional force in the spine. the spine, main- Back muscle Pivot T 12.0° R 200 N 350 N
258 TOPIC 8 | Rotat 23. BIO A person bending forward to lift a load "with his back" eg (Fig. P8.23a) 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 P8.23b of a person bend- ing forward to lift a 200.-N object. The spine and upper body are represented as a uniform horizontal rod of weight 350. N, pivoted at the base of the spine. The erector spinalis muscle, attached at a point two-thirds of the way up tains the position of the back. The angle between the spine and this muscle is 12.0°. Find (a) the tension in the back mus cle and (b) the compressional force in the spine. the spine, main- Back muscle Pivot T 12.0° R 200 N 350 N
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Transcribed Image Text:258 TOPIC 8 | Rotational Equilibrium and Dynamics
26. A
23. BIO A person bending forward to lift a load "with his back"
eg (Fig. P8.23a) 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 P8.23b of a person bend-
ing forward to lift a 200.-N object. The spine and upper body
are represented as a uniform horizontal rod of weight 350. N,
pivoted at the base of the spine. The erector spinalis muscle,
attached at a point two-thirds of the way up the spine, main-
tains the position of the back. The angle between the spine
and this muscle is 12.0°. Find (a) the tension in the back mus-
27.
cle and (b) the compressional force in the spine.
hadacu Back muscle0.0
ST
10
Pivot
* 12.0°
200N
350 N
Figure P8.23
Transcribed Image Text:Figure P8.27. Find the tension in each rope when a 700.-N
worker stands 1.00 m from one end? e2cm lon
ropes, as indicated by the blue vectors in
27. VA uniform plank of length 2.00 m and mass 30.0 ke
by three ropes, as indicated by the blue vectors in
supported
Figure P8.27. Find the tension in each rope when a 700 N
person is d = 0.500 m from the left end.
er of gravig fo
12, modeling rethooran
8 B of model
10.26 T,
T2
0.250
Theatthe le
40.0°
lid or boln vibbud
ns bano sdi svode m81 o
+ d »
3.
2.00 m
di In bas
rirob be ss gairda Figure P8.27
goil sdrto idgiod oh bail rel 2 00 bou d
28. A hungry bear weighing 700. N
walks out on a heam in
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