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Unformatted text preview: homework 11 – ALIBHAI, ZAHID 1 Latest unpenalized work: Apr 9 2007 Monday 04:00 (after this date you can not make a perfect score). Work cutoff: Apr 11 2007, 4:00 am. Question 1 part 1 of 1 10 points Nobody at the playground wants to play with an obnoxious boy, so he fashions a seesaw as shown so he can play by himself. Explain how this is done. 1. The angular velocity of the boy is can- celled with that of the board. 2. The weight of the boy is balanced with an unknown heavy metal. 3. The weight of the boy is balanced by the weight of the board. 4. The fulcrum is very far from the boy. Question 2 part 1 of 1 10 points Consider a solid sphere of radius R and mass m held against a wall by a string being pulled at an angle θ . mg P F θ R Determine the torque equation about the point P . 1. Rmg = RF 2. Rmg = 2 sin θ RF 3. Rmg = (2- sin θ ) RF 4. Rmg = (1 + cos θ ) RF 5. Rmg = (2- cos θ ) RF 6. Rmg = 2 cos θ RF 7. Rmg = (1 + sin θ ) RF Question 3 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 μ ≥ 1 2 tan θ . mg L f 45 ◦ b h b b F N μ = 0 . 4 The ladder will be 1. at the critical point of slipping. 2. stable. 3. unstable. Question 4 part 1 of 1 10 points A string provides a horizontal force which acts on a rectangular block of weight 420 N at top right-hand corner as shown in the figure homework 11 – ALIBHAI, ZAHID 2 below. 1m . 8 m F 420 N If the block slides with constant speed, find the tension in the string required to start to tip the block over. Answer in units of N. Question 5 part 1 of 1 10 points A 6m long, uniform ladder leans against a frictionless wall and makes an angle of 76 . 6 ◦ with the floor. The ladder has a mass M l = 21 . 3 kg. An M m = 55 . 38 kg man climbs 82% of the way to the top of the ladder when it slips and falls to the floor. What is the coefficient of static friction be- tween the ladder and the floor? Question 6 part 1 of 1 10 points Hint: Treat each half of the ladder sepa- rately. Assume: The floor is frictionless. The ladder is symmetric and forms an isosceles triangle. The stepladder has negligible weight and is constructed as shown in the figure below. The horizontal bar connecting the two legs of the ladder is pivoted half way up the ladder....
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