# HW9 - Pickering Tracey – Homework 9 – Due noon – Inst...

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Unformatted text preview: Pickering, Tracey – Homework 9 – Due: Feb 10 2006, noon – Inst: Drummond 1 This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 2) 10 points A string is tied to a book and pulled at an angle α as shown in the diagram. The book remains in contact with the table and does not move. m μ s F α Which choice best describes the free body diagram in the vertical direction for this situ- ation? 1. N = mg 2. N = mg + T cos α 3. N = mg- T cos α 4. N = mg + T sin α 5. N = mg- T sin α correct Explanation: m F s t r i n g α mg N μ s N Because the string is pulling partially up, the force of the table on the book (the normal force) is less than if the string were not there. X F y : N + T sin α = g N = mg- T sin α. 002 (part 2 of 2) 10 points Which forces change when the string is pulled so that the book moves as compared to when the book is stationary? 1. friction and tension in the string 2. tension in the string 3. friction 4. None of these 5. gravitational 6. normal, friction, and tension in the string correct 7. normal 8. normal and gravitational 9. friction, tension in the string, and gravi- tational Explanation: The string is taut, indicating a tension force that is not there when the string is loose. Looking at the answer to part 1, the normal force N is decreased by T sin α when the string is pulled with tension T ....
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HW9 - Pickering Tracey – Homework 9 – Due noon – Inst...

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