PHYS171_f11_lecture_42

# PHYS171_f11_lecture_42 - different To be in static...

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PHYS171 Chapter 11 Problem A cylindrical turntable of radius R , mass M rotates on a rigid, frictionless axle at angular frequency ω 0 . A piece of clay of mass m drops onto the turntable and sticks a distance r from the center. Find the final frequency of rotation. Determine change in kinetic energy. Determine if linear momentum is conserved. ( M =30kg, m=2.25kg, R =1.9m, r =1.8m, ω 0 =4 π )

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Chapter 12 Static Equilibrium and Elasticity Previously: For an object to be in equilibrium we must require that the sum of all forces is zero. Now: We are taking into account that objects are generally not point-like If an object is not rotating, then we must also require that the sum of all torques is zero. Chapter 12 Static Equilibrium and Elasticity O r F θ F r F r r r × = τ , = = 0 0 v v F
Chapter 12 Static Equilibrium and Elasticity O r F θ F r F r r r × = τ , = = 0 0 v v F If I choose a different axis the torque arising from the force F will be

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Unformatted text preview: different To be in static equilibrium, the net force must be zero and the net torque most be zero when evaluated about any axis. Chapter 12 Static Equilibrium and Elasticity O r F θ F r F r r r × = , r F If the net force is zero and the net torque is zero about any axis, it is zero about all possible axes. Chapter 12 Static Equilibrium and Elasticity mg F r F r r r × = τ , The center of gravity of an object is the same as the center of mass (in a uniform gravitation field). Therefore gravity doesn’t tend to rotate an object about its center of mass. It can rotate an object about an arbitrarily defined axis of rotation. mg mg mg Chapter 12 Problem You stand on a horizontal beam supported by a wire. Find the tension. θ m M, L x M = 20kg m = 60kg L = 8 m x = 2m θ = 53º...
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PHYS171_f11_lecture_42 - different To be in static...

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