By definition,
[tex]F = - \frac{dU}{dx} [/tex]
where U = potential energy
F = the force derived from the potential energy (PE).
For system 1, the PE is
U₁(x) = cx² + bx³
Therefore the force is
F₁(x) = -(2cx + 3bx²)
For system 2, the PE is
U₂(x) = a + cx² + bx³
Therefore the force is
F₂(x) = -(2cx + 3bx²)
Answer: The two forces are the same.