4.試求500N的作用力相對於點O的力矩之大小。

5.如圖三所示(Figure3) Determineθand the tension in the spring, which correspond to the equilibrium position of the spring. The unstretched length of spring is h and the constant of the spring is k. The pin and roller supporters are at A and C, respectively. The point load P works on B with the downward direction and neglect the weight of all objects. (20%)