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10-15-RotationalDynamicsII

# 10-15-RotationalDynamicsII - P Static Equilibrium Example...

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1 A 65-kg person stands on a lightweight ladder (the weight of the ladder is negligible). The floor is rough; hence it exerts both a normal force F N , and a frictional force f , on the ladder. The wall, on the other hand, is frictionless; it exerts only a normal force P on the ladder. Find the magnitudes of P , F N and f . W P F N f W Weight of the person: N s m kg mg W 637 ) / 8 . 9 )( 65 ( 2 Static Equilibrium: Example in Textbook p.346 P F N f W 0 , 0 , 0 y x F F Force x-comp y-comp P -P 0 W 0 -637N F N 0 F N f f 0 0 f P F x 0 637 N y F F N F N 637 Choose bottom of the ladder as rotational axis Torque by F N = 0, Torque by f = 0 Force lever arm torque P l for P W m 7 . 0 m 8 . 3 P m ) 8 . 3 ( Nm N m 446 ) 637 )( 7 . 0 ( +: counterclockwise - : clockwise 0 446 8 . 3 P N P 117 0 f P F x N f 117 (about any axis) l for W F N m 0 0 f m 0 0 (force F N goes through axis) (force f goes through axis) Plug into: N P 117 Solutions:

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