COLLEGE PHYS. VOL 1 LLF W/MODMAST >IC<
10th Edition
ISBN: 9781323149454
Author: YOUNG
Publisher: PEARSON C
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Chapter 10, Problem 48P
Pumping iron. A 72.0 kg weightlifter is doing arm raises using a 7.50 kg weight in her hand. Her arm pivots around the elbow joint, starting 40.0° below the horizontal. (See Figure 10.65.) Biometric measurements have shown that both forearms and the hands together 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 the weight is held 38.0 cm from the elbow joint. (a) Make a free-body 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?
Figure 10.65
Problem 48.
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Which of the following is the correct equation for Στ for the given rotation axis? All rotation axes lie on the x-axis and torques that would cause a counterclockwise rotation are positive.
Enter the letter(s) of the correct equation(s) in alphabetical order. For instance, if you thought that choices A, B, and D were correct, you would enter ABD.
Answer Choices:
Axis of Rotation
Et
A
x=0
(1/2)wL+F2d=0
B
x=L
(1/2)wL-F2(L-d)-F1L=0
C
x=0
(-1/2)wL+F2d=0
D
x=d
-F1d-F2(d-(1/2)L)=0
E
x=(1/2)L
(-1/2)F1L+F2(d-(1/2)L)
F
x=(1/2)L
(1/2)F1L+F2(d-(1/2)L)
Chapter 10 Solutions
COLLEGE PHYS. VOL 1 LLF W/MODMAST >IC<
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