A mass of \( 0.5 \, \text{kg} \) is attached to a spring with a spring constant \( k = 200 \, \text{N/m} \). The mass is displaced by \( 0.1 \, \text{m} \) from its equilibrium position. What is the potential energy stored in the spring?
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For potential energy stored in a spring, use the formula \( U = \frac{1}{2} k x^2 \), where \( k \) is the spring constant and \( x \) is the displacement from the equilibrium position.