고체역학 (Beer) — Principal Stresses Under a Given Loading: Problem 8.60

8.60 A vertical force P is applied at the center of the free end of cantilever beam \(AB\). (a) If the beam is installed with the web vertical (\(\beta = 0\)) and with its longitudinal axis \(AB\) horizontal, determine the magnitude of the force P for which the normal stress at point \(a\) is \(+120\text{ MPa}\). (b) Solve part \(a\), assuming that the beam is installed with \(\beta = 3^\circ\).