A refrigerator with a total mass of 30 kg is supported by springs with a total stiffness k N/m. The compressor, which contains a rotating unbalanced mass, rotates at 580 rev./min.
Determine the value of the spring constant k if only 10% of the shaking force of the unit is to be transmitted to the supporting structure. Assume the motion occurs in one direction only and there is no damping.

Solution As there is a reduction in force transmitted, the system must be operating above its natural frequency. As there is zero damping the phase angle must be 180^o

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David Grieve, 3rd February 2004.