The force F F\,F against extension x x\,x graph for a progressive spring being stretched is shown in the diagram.
What is the best estimate for the elastic strain energy stored in the spring when the extension is 20 mm?
0.32 J0.32\text{ J}0.32 J
0.53 J0.53\text{ J}0.53 J
0.80 J0.80\text{ J}0.80 J
1.60 J1.60\text{ J}1.60 J
