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Microsoft PowerPoint - Knight Ch 6 - dynamics I notes

# Microsoft PowerPoint - Knight Ch 6 - dynamics I notes -...

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1 Bodies in Equilibrium ( ___________ ) Remember this can occur if __________ or if v = ____________. Bodies in equilibrium, therefore, no ________ occurs Applying Newton’s 2 rd law, We will usually break these problems into components such that, = = 0 a m F r r = = 0 F 0 F y x r r Dynamics I - Chapter 6 Hints on Applying Newton’s Laws Bodies in Equilibrium ( a = 0) STRATEGY: 1. Diagram and givens converted to standard units 2. Draw free body diagram, identifying the _________ direction 3. Resolve forces into x and y components 4. Use equations of equilibrium 5. Solve simultaneous equations for unknowns = = 0 F and 0 F y x r r Don’t Stop Traffic! What is the tension in each wire if the traffic light weighs 20.0 N? Given: w = 20.0 N θ 1 = 30 o θ 2 = 40 o Wanted: T 1 , T 2 All units are in SI. Free body diagram: θ 1 = 30 o θ 2 = 40 o x y Don’t Stop Traffic! Using the equilibrium equations 0 40 cos 30 cos 2 1 = + = o o T T r r A B 0 0 . 20 643 . 0 500 . 0 0 0 . 20 40 sin 30 sin 0 0 . 20 sin sin 2 1 2 1 2 2 1 1 = + = = + = = + = N T T N T T N T T F o o y r r r r r r r θ θ = + = 0 cos cos 2 2 1 1 θ θ T T F x r r r 0 766 . 0 866 . 0 2 1 = + = T T r r ____________ ______________

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2 Don’t Stop Traffic! Solve for T 2 A 1 1 2 T 131 . 1 T 766 . 0 866 . 0 T r r r = = N 3 . 16 T N 0 . 20 T 23 . 1 N 0 . 20 T 727 . 0 T 500 . 0 N 0 . 20 ) T 131 . 1 ( 643 . 0 T 500 . 0 1 1 1 1 1 1 = = = + = + r r r r r r Plug into B C Plug T 1 into C N 4 . 18 ) N 3 . 16 ( 131 . 1 T 2 = = r Hints on Applying Newton’s Laws Bodies in non-equilibrium ( ______ ) Bodies feel a _____ force, therefore, motion occurs Applying Newton’s 2 nd law, We will usually break these problems into components such that, In cases of motion, we often have to include _____________ in our calculations. = a m F r r y y x x a m F a m F = = r r r r ____________ Hints on Applying Newton’s Laws Bodies in non-equilibrium ( a 0) STRATEGY: 1. Diagram and givens converted to standard units 2.
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