A small 20-kg block A is attached to the rod BC of negligible mass which is supported at B...

A small 20-kg block A is attached to the rod BC of negligible mass which is supported at B by a pin and bracket and at C by a spring of constant k = 2 kN/m. The system can move in a vertical plane and is in equilibrium when the rod is horizontal. The rod is acted upon at C by a periodic force P of magnitude P = Pm sin ωft, where Pm = 6 N. Knowing that b = 200 mm, determine the range of values of ωf for which the amplitude of vibration of block A exceeds 3.5 mm.

Fig. P19.103