QUIZ 9

1. A 200-N weight is supported by a uniform 135-N beam as shown in Fig. 1. Find the tension in the guy wire and the horizontal and vertical forces exerted by the hinge on the beam.

Solution. We write the first condition for the equilibrium of the system

                SFx = FH - FTcosq = 0;

                          FH - FTcos40°  = 0.

                SFy = FV + FTsinq  - mg - W =0.

                           FV + FTsin40°  - (135N) - 200N = 0.

                We write the second condition for the equilibrium of the system about the pivot point at hinge

                Sthinge= mg(1/2L) + WL - FTdsinq = 0;

                            (135N)(1.0m) + (200N)(2.0M) - FT(1.5m)sin40° = 0,

Which gives FT = 555N.

Solving the force equations we have

                   FH = 425N, FV = 22N.

  

2. When we turn the two blocks as shown in Fig 2, which one is in more stable equilibrium? Explain your answer.

 Solution. The left block is in stable equilibrium. As shown in figure, When the block rotates the gravitational force falls in the base. When the right block rotates the gravitational force is out of the base.