When a gymnast weighing 750 N executes the iron cross as in the figure below, th

Question

When a gymnast weighing 750 N executes the iron cross as in the figure below, the primary muscles involved in supporting this position are the latissimus dorsi ("lats") and the pectoralis major ("pecs"). The rings exert an upward force on the arms and support the weight of the gymnast. The force exerted by the shoulder joint on the arm is labeled Ft while the two muscles exert a total force Fn on the arm. Estimate the magnitude of the force Fm. Note that one ring supports half the weight of the gymnast, which is 375 N as indicated in part b of the figure. Assume that the force Fm acts at an angle of 45degreee below the horizontal at a distance of 4.0 cm from the shoulder joint. In your estimate, take the distance from the shoulder joint to the hand to be Z, = 70 cm and ignore the weight of the arm. In exercise physiology studies, it is sometimes important to determine the location of a person's center of gravity. This can be done with the arrangement shown in the figure below. A light plank rests on two scales that read FgX = 380 N and Fg2 = 320 N. The scales arc separated by a distance of 2.00 m. How far from the woman's feet is her center of gravity? 9. The Trans-Alaskan pipeline is 1,300 km long, reaching from Prudhoe Bay to the port of Valdez, and is subject to temperatures ranging from -73degreeeC to 35 degreeeC. How much does the steel pipeline expandjue to the difference temperature?

Explanation / Answer

In equilibrium

along vertical

Fnet = 0

Fg1 + Fg2 = W

W = 380+320 = 700 N

In equilibrium net torque = 0

Fg1*2 - W*xcm = 0

380*2 - 700*Xcm = 0

Xcm = (380*2)/700 = 1.08 from feet

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