Q$2)$ P$1($t$)($kN$)=15$cos$5$t

P$2($t$)($kN$)=10$cos$5$t

k $($kN$/$m$)=7645$

m $($t$)=20$

The following undamped shear frame is subjected to the harmonic

forces at the story levels. Determine the top story displacement $u_2$ by using

the Mode Superposition Method by considering only the first mode.

${}_1=\{0\mathrm{.}4,1{\}}^T$;$,{}_2=\{[-1,1]{\}}^T,w_1^2=\frac{3k}{5m}$;$,w_2^2=\frac{2k}{m}$