The maximum mass m 1 that a person can hold in a hand when the arm is positioned
ID: 1556405 • Letter: T
Question
The maximum mass m1 that a person can hold in a hand when the arm is positioned with a 1050 angle at the elbow as shown in is 21 kg. Assume the forearm and hand have a total mass of m2=3 kg with a center of gravity that is 15 cm from the elbow, and that the biceps muscle attaches 5 cm from the elbow.
a. What type of lever is illustrated in the figure?
b. Consider the arm keeps a horizontal position and apply the rotational equilibrium condition to determine the maximum force Fmax that the biceps muscle exerts on the forearm?
Fmax
Fg1
Fg2
Fmax
Explanation / Answer
a.
Class 3 lever . since the effort force is closer to the point of rotation
b.
Given data......
AB = 5 cm = 0.05 m
AC = 15 cm = 0.15 m
AD = 35 cm = 0.35 m
Fg2 = 3g = 3 x 9.8 = 29.4 N
Fg1 = m1 g = 21 x 9.8 = 205.8 N
using equilibrium of Torque about point A
Fmax (AB) Sin105 = Fg2 (AC) + Fg1 (AD)
Fmax (0.05) Sin105 = (29.4) (0.15) + (205.8) (0.35)
Fmax = 1592.5 N
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