An instrument known as an atomic force microscope (AFM) can be used to measure forces between atoms or molecules at the nanometer scale. Suppose you find the elasticity of biological membranes by measuring the indentation of the force probe into the membrane as a function of the applied force. You could then use an AFM to study the elastic properties of the capsid (outer shell) of a virus. The graph shows your data of the force applied to the capsid by the AFM (in nanonewtons) versus the indentation of the capsid (in nanometers). 

(a) What is the effective spring constant of the capsid for indentations of 0 to 14 nm? 

(b) How much elastic energy is stored in the membrane when it is indented 14 nm?

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1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0. 50 10 20 30 40 60 70 80 Indentation (nm) Applied force (nN)