# hmwk06 - Su (ycs73) – HW06 – Tsoi – (58020) 1 This...

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Unformatted text preview: Su (ycs73) – HW06 – Tsoi – (58020) 1 This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points An object having an initial momentum that may be represented by the vector below strikes an object that is initially at rest. Which of the following sets of vectors may represent the momenta of the two objects af- ter the collision? Note carefully: The original vector above and the following vectors are all drawn to the same length scale. 1. 2. 3. 4. 5. 6. correct 7. Explanation: There is no external force for the two-object system, so the total momentum is a constant. From the choices, applying the vector sum- mation for the momenta of the two objects, we can easily identify the correct choice. The figure below shows the sum of the x- and y-components of the vectors which repre- sent the correct answer. initial momentum The horizontal vectors add to be the same length as the vector presented in the question. The vertical vectors cancel, as expected, since there is no vertical momentum. 002 (part 1 of 2) 10.0 points Two blocks, A and B , are connected by a compressed spring. The mass of block A is twice that of block B . Immediately after release, compare the net force on block A to the net force on block B . The table is frictionless and the mass of the spring is zero. 1. F A,net and F A,net are both directed toward the left with F A,net larger than F A,net , but not Su (ycs73) – HW06 – Tsoi – (58020) 2 twice as large. Block A is pulling block B . 2. F A,net is equal in magnitude and opposite in direction to F B,net , and not zero. correct 3. F A,net will be in the opposite direction and half as large as F B,net . 4. F A,net is equal in magnitude and direction to F B,net , and not zero. 5. F B,net will be in the opposite direction and half as large as F A,net . 6. There is no net force on block A or block B . Explanation: F A,net is the force on block A from the spring, it’s reaction force is the force acting on the spring by block A , which we denote as F S,A . They have the same magnitude but they are in opposite directions. Similarly, F B,net has a reaction force F S,B . The total force on the spring vector F S,net = vector F S,A + vector F S,B =- vector F A,net- vector F B,net =- parenleftBig vector F A,net + vector F B,net parenrightBig = m spring · a = 0 · a = 0 . So that vector F A,net and vector F B,net must have the same magnitude but in opposite directions. Note: This is correct only when the mass of the spring can be neglected as mentioned in the problem. 003 (part 2 of 2) 10.0 points Which of the following best describes the sit- uation after the blocks are released?...
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## This note was uploaded on 04/15/2009 for the course PHY 58020 taught by Professor Tsoi during the Spring '09 term at University of Texas.

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hmwk06 - Su (ycs73) – HW06 – Tsoi – (58020) 1 This...

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