Answer
U = 13.0 J
Work Step by Step
From the previous problem (81g), we got that K = 1.0 J at x = 12.0 m. Since only conservative forces have acted on the particle, the original mechanical energy the particle had at x = 5.00 m, which was $E_{mec}$ = K + U = 14.0 J + 0 = 14.0 J, will remain the same. Therefore, we must have that at x = 12.0 m, U = 13.0 J, so that $E_{mec}$ = K + U = 1.0 J + 13.0 J = 14.0 J.
