Answer:The potential energy of a spring is given by the formula:PE = (1/2) * k * x^2Where: * PE is the potential energy * k is the force constant * x is the displacement from the equilibrium positionIn this case, the force constant (k) is given as 200 N/m. We are also told that the spring stretches by half its length. Let's assume the initial length of the spring is L. So, the displacement (x) is L/2.Initially, the potential energy is 20 J. We can use this information to find the initial displacement (x0):20 = (1/2) * 200 * x0^2x0^2 = 0.2x0 = sqrt(0.2)Now, we can find the final potential energy using the new displacement (x = L/2):PE_final = (1/2) * 200 * (L/2)^2PE_final = (1/2) * 200 * (1/4) * L^2PE_final = (1/8) * 200 * L^2Since we know that the initial displacement is sqrt(0.2), we can substitute this value into the equation for PE_final:PE_final = (1/8) * 200 * (sqrt(0.2))^2PE_final = (1/8) * 200 * 0.2PE_final = 5 JTherefore, the spring now has a potential energy of 5 J.