**A cord is 5.71e+1 meters long and 1.56 mm in diameter. When it supports a 1.41 kg load it stretches 3.50 cm.
What is the Young's modulus of the cord's material?**

length l = 5.71 x 10 m = 57.1 m

d = 1.56 mm = 1.56 x 10^{-3} m

r = 0.78 x 10^{-3}m

m = 1.41 kg

Increase in length Δl = 3.5 x 10^{-2} m

Area of cross section A = p (0.78 x 10 ^{-3})^{2} m^{2}

=1.91 x 10^{-6} m^{2}

Young's modulus Y = (F/A)/(Δl/l) = stress / strain = F l /A Δl

where F=mg=1.41 x 9.8 = 13.82

Y = (13.82 x 57.1)/(1.91 x 10^{-6} x 3.5 x ^{-2}) = 11.8 x 10^{9} N/m^{2}