The instrument is centered uniformly on a platform $P,$ which in turn is supported by four springs, each

spring having a stiffness of $130l\frac{b}{f}t.$ If the floor is subjected to a vibration of $7$ Hz and having a vertical

displacement of $0\mathrm{.}17$ ft $,$ determine the vertical displacement amplitude of the platform and instrument.

The instrument and the platform have a total weight of $18$ lb $.$

Ans: $1\mathrm{.}89$ in or $0\mathrm{.}157$ ft