Answer:
Part(a): The value of the spring constant is
.
Part(b): The work done by the variable force that stretches the collagen is
.
Explanation:
Part(a):
If '
' be the force constant and if due the application of a force '
' on the collagen '
' be it's increase in length, then from Hook's law

Also, Young's modulus of a material is given by

where '
' is the area of the material and '
' is the length.
Comparing equation (
) and (
) we can write

Here, we have to consider only the circular surface of the collagen as force is applied only perpendicular to this surface.
Substituting the given values in equation (
), we have

Part(b):
We know the amount of work done (
) on the collagen is stored as a potential energy (
) within it. Now, the amount of work done by the variable force that stretches the collagen can be written as

Substituting all the values, we can write

You haven't included the list of choices that goes with the question, so it's
impossible for me to choose the correct one, or to help you choose it.
Regarding my ability to answer the question and collect the 5-point bounty,
I'm free to make up any phrase of my own that correctly describes an atom.
-- very very very very very very very tiny
-- includes even tinier particles, with electric charges
both positive and negative
-- smaller than the wavelength of visible light
Density = mass/volume. 5000/50= 100 grams per cubic centimeter. No substance on Earth has anywhere near that density. Tops is about 20 for osmium and gold.