When holding the 4. 8 - lb stone in equilibrium, the humerus H, assumed to be sm

Question

When holding the 4. 8 - lb stone in equilibrium, the humerus H, assumed to be smooth, exerts normal forces Fc and FA on the radius C and ulna A as shown. (Figure 1) Determine the force Fc that the humerus H exerts on the radius C Neglect the weight of the arm. Express your answer to three significant figures and include the appropriate units. Determine the force FA that the humerus H exerts on the ulna A. Neglect the weight of the arm. Express your answer to three significant figures and include the appropriate units. Determine the force FB that the biceps B exerts on the radius C for equilibrium. Neglect the weight of the arm. Express your answer to three significant figures and include the appropriate units.

Explanation / Answer

at equilibrium of the hand after holding 4.8 lb of weight.

Fx =0

Fy = 0

MC = 0 (+ve counter clockwise)

for Fx =0

Fc - FB*cos75 = 0

Fc = FB*cos75 .....(1)

for Fy = 0

-FA+FB*sin75-4.8 =0

FB*sin75 - FA = 4.8    ......(2)

for MC = 0

+(FB*sin75)*(2-0.8)+FA*0.8 - 4.8*(14-0.8)=0

(FB*sin75)*1.2+FA*0.8 = 4.8*13.2 .....(3)

after solving equation (2) and Equation (3), we get;

FA = 28.8 lb

put FA = 28.8 lb in the equation (2), we can get;

FB = 34.785 lb

put FB=34.785 in the equation (1), we can get;

FC = 9 lb

hence,

FA= 28.8 lb

FB= 34.785 lb

FC= 9 lb

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