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903 Chapter 12 Static Equilibrium and Elasticity Conceptual Problems 1 •(a) False. The conditions ∑=ii0Frand ∑=ii0τrmust be satisfied. (b) True. The necessary and sufficient conditions for static equilibrium are ∑=ii0Frand ∑=ii0τr. (c) True. The conditions ∑=ii0Frand ∑=ii0τrmust be satisfied. (d) False. An object is in equilibrium provided the conditions ∑=ii0Frand ∑=ii0τrare satisfied. 2 •False. The location of the center of gravity depends on the mass distribution. 3 •No. The definition of the center of gravity does not require that there be any material at its location. 4 •Determine the ConceptWhen the acceleration of gravity is not constant over an object, the center of gravity is the pivot point for balance.5••Determine the Concept This technique works because the center of mass must be directly under the balance point. Thus, a line drawn straight downward will pass through the center of mass, and another line drawn straight downward when the figure is hanging from another point will also pass through the center of mass. The center of mass is where the lines cross.*6 •Determine the Concept No. Because the floor can exert no horizontal force, neither can the wall. Consequently, the friction force between the wall and the ladder is zero regardless of the coefficient of friction between the wall and the ladder.
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