A freely running motor rests on a thick rubber pad to reduce vibration. The motor sinks $$h=10~\mbox{cm}$$ into the pad. Estimate the rotational speed in RPM (revolutions per minute) at which the motor will exhibit the largest vertical vibration.

Details and assumptions

• The gravitational acceleration is $$g=9.8~\mbox{m/s}^2$$.
• Treat the rubber pad as a spring.
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