Determine whether the following models are stable, unstable, or neutrally stable. 4x + 6x = 7

a) A two-degree-of-freedom coupled pendulum model is shown in Figure Q1a. The parameters of the model are: k=100 N/m; m=10 kg and L=1 m. The equations of motion of the system are given below. J₁ä + (mgL + kĽ² ) 8₁ - kľ² 0₁₂ = 0 J₁₂+(mgL+kĽ²)₂-kĽ² 0₁ = 0 i) Calculate the natural frequencies. ii) Draw the mode shapes. m Figure Q1a. b) In the above system discuss the implications of the following changes in coupling stiffness. i) k is reduced considerably to 0.1 N/m. ii) k is increased considerably to 1x105 N/m. c) Draw a schematic of modal test arrangement of a beam using instrumented impact hammer. d) Why is it necessary to measure force in a modal test?

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All values equal to 1

For point a, suggest a different form but the same equation without removing u

The dependence of the tensions t (units: N) in a structure on the external forces f (units: N) follows the linear system Ct=f, where both t and f are 5 by 1 column vectors. The coefficient matrix C has been determined to be [ 11 14 20 -5 -19 ] -5 7 -3 5 -6 4 -5 13 -2 -10 0 0 0 12 -10 0 0 0 0 14 By how many N would the external force f2 need to be decreased (while all other external forces stay the same) in order to decrease the tension t3 by 94 N?

2- Derive the rule-of-mixtures expression for the composite extensional modulus E₁ assuming the existence of an interphase region. The starting point for the derivation would be the model shown below. For simplicity, assume the interphase, like the matrix, is isotropic with modulus E¹. With an interphase region there is a volume fraction associated with the interphase (i.e.,V;). For this situation: vf + vm + vi = 1 H |w²||wm|

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Derive the rule-of-mixtures expression for the composite extensional modulus E₁ assuming the existence of an interphase region. The starting point for the derivation would be the model shown below. For simplicity, assume the interphase, like the matrix, is isotropic with modulus E¹. With an interphase region there is a volume fraction associated with the interphase (i.e.,V;). For this situation: vf + vm + Vi = 1 wi |||||||