According to one set of measurements, the tensile strength of hair is 196MPa , w

Question

According to one set of measurements, the tensile strength of hair is 196MPa , which produces a maximum strain of 0.320 in the hair. The thickness of hair varies considerably, but let's use a diameter of 47.0 um . Part A What is the magnitude of the force giving this tensile stress? Express your answer using two significant figures. = N Part B If the length of a strand of the hair is 11.0cm at its breaking point, what was its unstressed length? Express your answer using two significant figures. = cm

Explanation / Answer

According to one set of measurements, the tensile strength of hair is 196MPa , which produces a maximum strain of 0.320 in the hair. The thickness of hair varies considerably, but let's use a diameter of 47.0 um . Part A What is the magnitude of the force giving this tensile stress?

I agree with your answer for (A)

Strain = [change in length] / [unstressed length]

You are given that the maximum strain is 0.400

call the unstressed length x

[Strain has no units, so just this once, we can work in cm, rather than converting to m]

The change in length = (12 - x)

So 0.400 = (12 - x) / x

multiply both sides by x

0.400x = 12 - x
1.400x = 12
x = 12/1.400
x = 8.571 cm

Express your answer using two significant figures. = N Part B If the length of a strand of the hair is 11.0cm at its breaking point, what was its unstressed length? Express your answer using two significant figures. = cm

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