
Concept explainers
The two homogeneous bars AB and BC are connected with a pin at B and placed between rough vertical walls. If the coefficient of static friction between each bar and the wall is 0.25, determine the largest angle 6 for which the assembly will remain at rest.

Largest angle θ for which the assembly will remain at rest
Answer to Problem 7.4P
The largest angle θ is equal to 6.75°.
Explanation of Solution
Given information:
Co-efficient of static friction between each bar and wall is 0.25.
For impending sliding, the friction force equals its limiting value;
F=Fmax=μsN
μs - Co-efficient of static friction
Steps to follow in the equilibrium analysis of a body are:
1. Draw the free body diagram.
2. Write the equilibrium equations.
3. Solve the equations for the unknowns.
Calculation:
FBD of assembly
Assume NA,NC as the reaction force at point A and C.
Assume FA,FC as the friction force at point A and C.
For the equilibrium of entire section, the bending moment about point A is equal to zero.
∑MA=0
FC((48 in)cosθ)−(8 lb)((12 in)cosθ)−(10 lb)((36 in)cosθ)=0
Solve
48FC−96−360=0 FC=9.5 lb
Write equilibrium equation in vertical direction.
↑∑Fy=0
FA+FC−(8 lb)−(10 lb)=0 FA=8.5 lb
Write equilibrium equation in horizontal direction.
→∑Fx=0
NA−NC=0 NA=NC
The impending sliding will first occur at point C.
FCNC>FANA
The reaction force NC at point C
NC=FC0.25 =9.5 lb0.25 =38 lb
FBD of bar BC
For the equilibrium of above section, the bending moment about point B is equal to zero.
∑MB=0
FC((24 in)cosθ)−NC((24 in)sinθ)−(10 lb)((12 in)cosθ)=0 9.5(24cosθ)−38(24sinθ)−10(12cosθ)=0 108cosθ−912sinθ=0
Therefore
θ=tan−1(108912) =6.75°
Conclusion:
The largest angle θ is equal to 6.75°.
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Chapter 7 Solutions
International Edition---engineering Mechanics: Statics, 4th Edition
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- International Edition---engineering Mechanics: St...Mechanical EngineeringISBN:9781305501607Author:Andrew Pytel And Jaan KiusalaasPublisher:CENGAGE L
