## College Physics (4th Edition)

Since the diameter is twice the radius, the diameter of the hair is $8.7\times 10^{-5}~m$
We can find the radius: $\frac{F}{A} = 2.0\times 10^8~N/m^2$ $A = \frac{F}{2.0\times 10^8~N/m^2}$ $\pi~r^2 = \frac{F}{2.0\times 10^8~N/m^2}$ $r = \sqrt{\frac{F}{(\pi)(2.0\times 10^8~N/m^2)}}$ $r = \sqrt{\frac{1.2~N}{(\pi)(2.0\times 10^8~N/m^2)}}$ $r = 4.37\times 10^{-5}~m$ Since the diameter is twice the radius, the diameter of the hair is $8.7\times 10^{-5}~m$