A vertically upward force, F, is applied at C of horizontal link 4, which is pinned to the ground at B and pinned to vertical links 2 and 3 at A. Lengths AB = 2 ft and AC = 5 ft and the three links are made from a steel alloy with a compressive yield strength Syc = 60 000 psi and a modulus of elasticity E = 30 × 106 psi. Link 2 has a hollow circular cross section with an outside diameter D = 2 in, wall thickness t = 0.25 in, and length L = 5 ft. Using the theoretic value for the end-condition constant for link 2, determine:

(a) the value of the slenderness ratio at the point of tangency between the Euler-column formula and the Johnson parabolic formula;

(b) the critical load acting on link 2; and

(c) the force, F, for the factor of safety of link 2 to guard against buckling to be N = 1.

(d) If link 2 has a solid circular cross section with diameter D = 3 in and F = 20 000 lb, then determine the maximum length of link 2 for the factor of safety to guard against buckling to be N = 2.