A ground retaining wall is shown in Fig. 9–36a. The ground, particularly when wet, can exert a significant force F on the wall. (a) What force produces the torque to keep the wall upright? (b) Explain why the retaining wall in Fig. 9–36b would be much less likely to overturn than that in Fig. 9–36a. -F (a) (b) FIGURE 9-36 Question 5.

- 5. Two identical, uniform beams of length 3 m and weighing 260 N each are connected at one end by a frictionless hinge. A light horizontal crossbar, attached at the midpoints of the beams maintains an angle 50° between the beams. The beams are suspended from the ceiling by vertical wires so they form a V. See figure. (a) What force does the crossbar exert on each beam? (b) Is the crossbar under compression or tension, i.e. are the ends of the crossbar being pushed together or stretched farther apart? (c) What force (magnitude and direction) does the hinge exert on each beam? Crossbar Hinge

The uniform 19.0 kg beam below is 6.4 m long and is perfectly balanced about a point 1.4 m from the left end. What is the mass of the block? (Hint: when calculating the torque due to the weight of the beam, consider all of its mass to be located at its center of mass.)

Why is it not possible to sit upright in a chair and rise toyour feet without first leaning forward?