4. -1 points OSColPhys2016 5.3.WA.037 My Notes Ask Your Teacher During a circus

Question

4. -1 points OSColPhys2016 5.3.WA.037 My Notes Ask Your Teacher During a circus act, one performer swings upside down hanging from a trapeze holding another, also upside down, performer by the legs. If the upward force on the lower performer is three times her weight, how much does each of the bones (the femurs) in her upper legs stretch? You may assume each is equivalent to a uniform rod 35.0 cm long and 1.80 cm in radius. Her mass is 55.1 kg. Assume Young's modulus for bone under tension is 16 10 N/m2 Additional Materials Reading

Explanation / Answer

change in length L = 1/y*f/A*L0

here L0 = 0.35 m

A = pir^2 = 3.14*0.018^2 = 1.018*10^-3 m^2

y = 1.6*10^10 N/m^2

f tot = 3w = 3*55.1*9.8 = 1619.94 N

fleg = ftot/2 = 809.97 N

L = 1/1.6*10^10*809.97*0.35/1.018*10^-3 = 0.174*10^-4 m

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