12 Static Equilibrium and Elasticity

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12 Static Equilibrium and Elasticity

• Conditions for Equilibrium
• The Center of Gravity
• Some Examples of Static Equilibrium
• Stress and Strain
• (accelerated frame, indeterminate)
• Hk 19, 21, 23, 31, 33, 41.

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Conditions for Equilibrium
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Center of Gravity, cg

• center of gravity the average location of weight

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12-3Some Examples of Static Equilibrium
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Q A 70kg student lies along a board with a
fulcrum at one end and a scale 2.0m away at the
other end. The top of his head is directly above
the fulcrum. When he is on the board as described
the scale reading is 250N more than when he is
off the board. Where is the cg of the student?
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Stress and Strain
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Q What shortening of a 50cm diameter concrete
pillar occurs when a 20 000 kg truck is balanced
on top of it? What is the maximum load in kg?
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A cube 50cm per side suffers shear strain of 1
when a shear force of 10 000N is applied along
two opposite faces. What is the shear modulus of
this material?
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End
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normal force on wheel ? 0
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Summary