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HWS09_13 - these forces compare with the weights of the...

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P1112 Spring 2009 Homework #13 due second section of week of April 20. Solutions posted Friday April 24. Quiz on HW #13 first section of week of April 27. Reading: 10.7, 11.1-11.3, 13.1 – 13.3 Not all concepts will be covered in class – you are responsible for all material in the reading and in the homework problems. Problems (several are short) : 1. Y&F 10.51 (a) – (d) Modifying a Gyroscope. 2. A person bends over and lifts a 50 lb object with their back in the horizontal position (a terrible way to lift something! We'll see why in this problem). The back muscle, attached at a point two-thirds up the spine from the hip pivot, maintains the position of the back, where the angle between the spine and this muscle is 12°. Using the simplified mechanical model in the diagram on the right and taking the weight of the upper body to be 80 lb, find (a) the tension in the back muscle [Ans: 650 lb] (b) How do
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Unformatted text preview: these forces compare with the weights of the object and the upper body? 3. Y&F 11.73 The farmyard gate. 4. A ladder 5.0 m long rests against a frictionless vertical wall with its lower end 3.0 m from the wall. The ladder weighs 160 N. The coefficient of static friction between the foot of the ladder and the ground is 0.40. A man weighing 740 N climbs slowly up the ladder. (a) What is the maximum frictional force that the ground can exert on the ladder at its lower end? (b) What is the actual frictional force when the man has climbed 1.0 m along the ladder? (c) how far along the ladder can the man climb before it starts to slip? 5. Y&F 11.77 Box on a conveyor belt. 6. Y&F 13.7 Mass and spring. 7. Y&F 13.15 Weighing an astronaut in space. 8. Y&F 13.18 Mass and spring. Also draw a graph of v x ( t ) as a function of time, over two periods....
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