Related questions
A 72.0 kg weightlifter doing arm
raises holds a 7.50 kg weight.
Her arm pivots around the
elbow joint, starting 40.0° below
the horizontal (Fig.).
Biometric measurements have
shown that, together, the forearms
and the hands account for 6.00%
of a person’s weight. Since the
upper arm is held vertically, the
biceps muscle always acts vertically
and is attached to the bones
of the forearm 5.50 cm from the
elbow joint. The center of mass of this person’s forearm–
hand combination
is 16.0 cm from the elbow joint, along the bones of the forearm,
and she holds the weight 38.0 cm from her elbow joint. (a) Draw a freebody
diagram of the forearm. (b) What force does the biceps muscle
exert on the forearm? (c) Find the magnitude and direction of the force
that the elbow joint exerts on the forearm. (d) As the weightlifter raises
her arm toward a horizontal position, will the force in the biceps muscle
increase, decrease, or stay the same? Why?
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