Question
(a) Under these circumstances, what maximum weight would you attempt to lift?
_______N
(b) What force would your biceps apply while lifting this weight?
_________ N
F = _____ N
R = ______ N EXAMPLE 8.6 A Weighted Forearm GOAL. Apply the equilibrium conditions to Humerus the human body. 50.0 N Biceps PROBLEM A 50.0-N 11 b) bowling ball is held in a person's hand Ulna. with the forearm horizontal, as in Figure 0.0300 m (a). The biceps muscle 50.0 N is attached 0.0300 m 0.0300 m 0,350 m from the joint, and the 0.350 m ball is 0,350 m from the joint. Find the upward A weight held with the fo force F exerted by the adel for the biceps on the forearm (the ulna and the downward force R exerted by the humerus on the forearm, acting at the joint. Neglect the weight of the forearm and slight deviation from the vertical of the biceps STRATEGY The forces acting on the forearm are equivalent to those acting on a bar of length 0.350 m, as shown in Figure (b). Choose the usual x- and coordinates as shown and the axis at O on the left end. (This completes steps 1 and 2.) Use the conditions of equilibrium to generate equations for the unknowns, and solve.
Explanation / Answer
a)
W = 54.6 N
d = 0.02910 m
l = 0.340 m
using
F X d = W X l
F = W X l / d
F = 54.6 X 0.34 / 0.0291
F = 637.93 N
F = W + R
637.93 = 54.6 + R
R = 583.33 N
R X d - ( l - d ) X W = 0
583.33 X 0.0291 - ( 0.34 - 0.0291 ) X W = 0
W = 54.599 N
b )
Fbicep - R - W = 0
Fbicep = R + W
Fbicep = 583.33 + 54.6
Fbicep = 637.93 N
