Theory of Machine
A body is said to be under forced vibrations, when

There is a reduction in amplitude after every cycle of vibration
No external force acts on a body, after giving it an initial displacement
A body vibrates under the influence of external force
None of these

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Theory of Machine
In a steam engine, the earlier cut-off with a simple slide valve may be obtained by increasing the steam lap and the angle of advance of the eccentric but keeping constant the travel and lead of the valve, this method will

Reduce length of effective stroke of piston
All of the listed here
Reduce maximum opening of port to steam
Cause withdrawing or throttling of steam

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