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Unformatted text preview: oldhomewk 29 YOO, HEE Due: Apr 28 2008, 4:00 am 1 Question 1, chap 14, sect 1. part 1 of 1 10 points A ladder is leaning against a smooth wall. There is friction between the ladder and the floor, which may hold the ladder in place; the ladder is stable when 1 2 tan . mg L f 45 b h b b F N = 0 . 4 The ladder will be 1. stable. 2. at the critical point of slipping. 3. unstable. correct Explanation: Stability requires 1 2 tan 45 = 0 . 5 . Since = 0 . 04 < . 5 , the ladder is unstable. keywords: static equilibrium, instability Question 2, chap 14, sect 3. part 1 of 3 10 points A uniform rod pivoted at one end point O is free to swing in a vertical plane in a gravitational field. However, it is held in equilibrium by a force F at its other end. x y F F x F y W R x R R y O Force vectors are drawn to scale. What is the condition for translational equilibrium along the horizontal x direction? 1. R x F x sin = 0 2. F x = 0 3. R x F x cos = 0 4. R x + F x = 0 correct 5. F x cos R x sin = 0 Explanation: Using the distances, angles and forces de- picted in the figure, the condition summationdisplay F x = 0 for translational equilibrium in the x direction gives R x + F x = 0 . Question 3, chap 14, sect 3. part 2 of 3 10 points What is the condition for translational equilibrium along the vertical y direction? 1. R y + F y W = 0 correct 2. W R y + F y = 0 3. R y F y + W = 0 4. R y + F y = 0 5. R y sin + F y sin W cos = 0 Explanation: oldhomewk 29 YOO, HEE Due: Apr 28 2008, 4:00 am 2 For the equilibrium in the y direction, summationdisplay F y = 0 gives R y + F y W = 0 ....
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