Answer
U = 12.0 J
Work Step by Step
From Problem 81e, we had that at x = 11.0 m, K = 2.00 J. Since only conservative forces have acted on the particle, the original mechanical energy at x = 5.00 m, which was $E_{mec}$ = K + U = 14.0 J + 0 = 14.0 J, will be conserved. Therefore, we must have U = 12.0 J, so that $E_{mec}$ = K + U = 2.0 J + 12.0 J = 14.0 J.
