The figure below shows an outstretched arm (0.61 m in length) that is parallel to the floor. The arm is pulling downward against the ring attached to the pulley system, in order to hold the 98 N weight stationary. To pull the arm downward, the latissimus dorsi muscle applies the force M in the figure, at a point that is 0.069 m from the should joint and oriented at an angle of 29°. The arm has a weight of 47 N and a center of gravity (cg) that is located 0.28 m from the shoulder joint.
The figure below shows an outstretched arm (0.61 m in length) that is parallel to the floor. The arm is pulling downward against the ring attached to the pulley system, in order to hold the 98 N weight stationary. To pull the arm downward, the latissimus dorsi muscle applies the force M in the figure, at a point that is 0.069 m from the should joint and oriented at an angle of 29°. The arm has a weight of 47 N and a center of gravity (cg) that is located 0.28 m from the shoulder joint.
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Transcribed Image Text:The figure below shows an outstretched arm (0.61 m in length) that is parallel to the
floor. The arm is pulling downward against the ring attached to the pulley system, in
order to hold the 98 N weight stationary. To pull the arm downward, the latissimus
dorsi muscle applies the force M in the figure, at a point that is 0.069 m from the
should joint and oriented at an angle of 29°. The arm has a weight of 47 N and a center
of gravity (cg) that is located 0.28 m from the shoulder joint.
0.61 m
0.28 m
0.069 m
Axis at
98 N
shoulder
joint
cg
29
Aldentify all the forces on the arm and draw an accurate and complete
free body diagram on both the arm and the 98 N weight. You may draw on the
figure if you wish.
B Write down the correct equation of motion ON THE 98 N WEIGHT by
summing all the forces acting on it using Newton's 2nd Law of Motion. You must
identify and draw your chosen coordinate system.
( Write down the correct equation of motion ON THE ARM by summing
all the forces acting on it using Newton's 2nd Law of Motion. You must identify
and draw your chosen positive direction for the torque. (Note: The direction of
the torque is not the same as the direction of rotation. Watch the relevant
exercise videos again if you're not sure, and carefully listen to what I am saying
about the direction of rotation and the direction of the torque.).
D How are the force due to the string on the hand related to the force by
string on the block related? Which law of Newton describes this relationship?
E Solve for the magnitude of M.
FInterpret this result. In other words, is this a significant amount of force
for a single set of muscles just to be able to hold the weight down?
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