An 18-lb block A slides in a vertical frictionless slot and is connected to a moving suppo...

An 18-lb block A slides in a vertical frictionless slot and is connected to a moving support B by means of a spring AB of constant k = 8 lb/ft. Knowing that the acceleration of the support is a = am sin ωft, where am = 5 ft/s2 and ωf = 6 rad/s, determine (a) the maximum displacement of block A, (b) the amplitude of the fluctuating force exerted by the spring on the block.

Fig. P19.111