tensile strength - 10 points first correct answer!?

Question

A human hair breaks under a tension force of 1.2 N. If the tensile strength of human hair is about 2.0x108 Pa, what is the diameter of the hair in microns (10-6m)?

Answer 1

Ok, just remember :

Tensile strenght = Force / Surface :

2*10^8 = 1.2 / Surface

Surface = 0.6*10^-8 m^2

But, if we consider that, as the surface of a circle :

0.6*10^-8 = pi*r^2

r = sqrt(0.2*10^-8) = 0.4*10^-4

diameter = 2r = 0.8*10^-4

In microns : 80 uM >>> microns

Answer 2

6*10^-9 meters

1.2 / (2.0*10^8) = 6*10^-9 meters


---Wait, that's the area of the hair, not the diameter.