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Consider a reciprocating engine with crank length \(L\). The secondary unbalance force due to a virtual crank of radius \(L/4\) rotating at twice the engine speed is

1. radius = \(L^2/4R\) rotating at half the engine speed
2. radius = \(R\) rotating at half the engine speed
3. radius = \(L/4\) rotating at half the engine speed
4. radius = \(L/2\) rotating at half the engine speed

Correct answer: radius = \(L/4\) rotating at half the engine speed

Solution

In balancing of reciprocating masses, the secondary force is represented by a virtual crank of radius \(r/4\) rotating at twice the engine speed. Here the crank length is \(L\), so the equivalent virtual crank has radius \(L/4\) and rotates at twice the engine speed. The correct option matches this representation.

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