Difficulty: Easy
Correct Answer: horizontal surface
Explanation:
Introduction / Context:
Equilibrium classification (stable, unstable, neutral) is widely used in mechanics and machine design. A body is in neutral equilibrium if its potential energy remains unchanged for small displacements; it neither returns to the original position nor moves away.
Given Data / Assumptions:
Concept / Approach:
If the height of the cylinder’s centre remains the same for small movements, the gravitational potential energy remains constant. That is the definition of neutral equilibrium. On a truly horizontal plane, when a smooth cylinder rolls or slides slightly, the centre stays at the same height.
Step-by-Step Solution:
Verification / Alternative check:
Contrast with other surfaces: on a convex support, the centre height changes with small rolls, usually increasing initially (unstable). In a concave cradle, height decreases and then increases, creating a restoring tendency (stable).
Why Other Options Are Wrong:
Common Pitfalls:
Assuming “smooth” implies stability. Smoothness removes friction but does not by itself decide stability; the geometry and centre-height variation do.
Final Answer:
horizontal surface
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