Answer:
[tex]U(3)=-43J[/tex]
Explanation:
Potential energy is minus the integral of Fdx. Doing the integration yields:
[tex]U=\int\limits {6.0x+12}\, dx[/tex]
[tex]U=-3x^2-12x+C[/tex]
[tex]U(0)=20J[/tex]
so
[tex]U(0)=-3(0)^2+12(0)+C=20[/tex]
[tex]C=20[/tex]
Now for x=3.0m
[tex]U(3)=-3*(3)^2-12(3)+20[/tex]
[tex]U(3)=-43J[/tex]