### **Gravitational Force Comparison**
In a universe where gravity follows an inverse cube law ($ F \propto 1/r^3 $), doubling the distance ($ r \to 2r $) reduces the gravitational force by a factor of $ 1/(2)^3 = 1/8 $. Thus, the new force is **1/8th of the original**.

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### **Outcome for the Planet's Orbit**
1. **Required Centripetal Force**:  
   For a circular orbit, the gravitational force must balance the centripetal force. In this universe, the orbital velocity $ v \propto 1/r $, so the required velocity for a circular orbit at $ 2r $ is **half** the original velocity ($ v_{\text{new}} = v_{\text{old}}/2 $).

2. **Effect of the Sudden Push**:  
   If the planet is suddenly moved to $ 2r $ without adjusting its velocity, its speed remains $ v_{\text{old}} $. This velocity is **too high** for the weaker gravitational force at $ 2r $, causing the planet to experience **insufficient centripetal force** to maintain a circular orbit.

3. **Resulting Orbit**:  
   The planet will enter an **elliptical orbit** or escape the system entirely. The imbalance between the gravitational force and the planet's inertia leads to an unstable trajectory. Inverse cube forces generally do not support stable closed orbits (per Bertrand’s theorem), so the planet is unlikely to settle into a new circular orbit. Instead, it would follow a **spiral or hyperbolic path**, depending on the energy imparted by the push.

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### **Conclusion**
- **New Gravitational Force**: $ \frac{1}{8} $ of the original.  
- **Orbit Outcome**: The planet’s orbit becomes unstable, likely transitioning to an elliptical or unbound trajectory due to the mismatch between its velocity and the weakened gravitational force.