The sport of gymnastics requires both impressive physical strength and extensive

Question

The sport of gymnastics requires both impressive physical strength and extensive training for balance. The iron cross is an exercise performed on two suspended rings, which the gymnast grips with his hands. Suppose that a male gymnast wishes to execute an iron cross during a gymnastics session (see figure 6.39 in text). The total mass of the gymnast is 57 kg. Each ring supports half of the gymnast's weight. Assume that the weight of one of his arms is 5% of his total body weight. The distance from his shoulder joint to where his hand holds the ring is 56 cm. The distance tfrom his hand to the center of mass of his arm is 38 cm. The horizontal distance from his shoulder to the middle of his chest, directly above the center of mass of his body is 22 cm. If the gymnast is still, how much force and torque are at one of his shoulder joints?

Diagram:http://www.ruf.rice.edu/~bioewhit/foundations/bioe252/docs/Ch 6_files/image002.jpg

Explanation / Answer

balancing the forces gravitational force =57 *9.8 = 558.6 N so force on each ring = 558.6 /2 = 279.3 N balncing the torque making the shoulder joint as the centre . the mass of the shoulder joint = 0.05*57 = 2.85 kg so force of gravitation on shoulder due to its weight = 2.85*9.8 = 28.215 N so the force at the shoulder joints be F balancing the forces we get the F = 279.3 - 28.215 N = 251 N torque = 279.3*(56^2-38^2)*10^-4 =47.2 N-m cheers :) )

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