Read a Breaking Rod: Preserve the Instantaneous Motion
A released rod first follows rigid-body rotation about its pivot. If it breaks without impulse, each piece inherits its centre-of-mass velocity and angular velocity at that instant.
Motion and force questions become simpler when direction, starting condition, time and the acting forces are marked first.
Start with the condition
Use energy from horizontal to vertical for the pre-break angular speed. For each half after break, combine translational and rotational kinetic energy to determine its subsequent rise or rotation.
Build the governing relation
Check the small-oscillation period from I-pivot/(Mg d), where d is centre-of-mass distance from pivot; this differs from the simple-pendulum length formula.
Finish with a physical check
Check the limiting case before selecting an option: remove the special feature in the diagram or make the relevant parameter very large or very small. The result should reduce to a familiar relation.
OlympIQ exam lens
- ✓State the physical condition before choosing a formula.
- ✓Keep direction, sign and constraint information explicit.
- ✓Test one limiting case before committing to an option.
Assuming each half is instantaneously at rest after break violates continuity of velocity when no impulse is supplied.
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