2009 Midterm with solutions

2009 Midterm with - PHYS 131 MIDTERM October 26th 2009 WITH SOLUTIONS-The exam comprises two parts 6 short-answer questions and 4 problems

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PHYS 131 MIDTERM October 26 th , 2009 --- WITH SOLUTIONS --- The exam comprises two parts: 6 short-answer questions, and 4 problems. Calculators are allowed, as well as a formula sheet (one-side of an 8½” x 11” sheet) of your own making. Answer all the short-answer questions with a few words or a phrase, but be concise, please! For the problems, your grade will be calculated with the best three problems . Show your work. The short answer problems are worth four points each, and the problems are worth 10 points each. Put all answers in the red and white answer booklets provided; you may keep this exam. Good luck ! Short answer questions (answer all): you should not need to do any calculations for these questions. Answer in a few words, a short phrase, or a simple sketch. 1) [4 pts] Make a sketch of a velocity-vs-time graph where the velocity is always positive but the acceleration is always negative. Give a physical example of such a system. Solution: A physical example would be a car moving towards a stop sign and decelerating, or a ball thrown upwards towards someone in a window. Example graph (acceleration < 0 means slope must always be <0, while the v is always positive): 2) [4 pts] In the diagram below, blocks 1 and 2 are identical, and the surface that block 1 is resting upon is frictionless. The two blocks are connected by a massless string running over a pulley. Initially block 2 is at rest (with the string taut) at the same height as block 1, and equidistant from the pulley. Then block 2 is dropped. Phys 131 Midterm, Oct 26 th , 2009
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a) Draw the free-body diagram for each block after block 2 is dropped, but before it hits. b) Does block 1 hit the pulley before or after block 2 hits the wall? No calculations are necessary! Solution: (a) The free-body diagrams are: (b) Block 1 hits first. The tensions are equal, but in Block 2’s case, it acts at an angle. So the horizontal force (the only force that can make Block 2 move towards the wall) is smaller in Block 2’s case than for Block 1. Hence, Block 1 has the larger acceleration and will hit the pulley before Block 2 hits the wall. 3) [4 pts] The plot below shows the potential energy function U vs. x. Identify the numbered
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This note was uploaded on 10/11/2011 for the course SCIENCE 131 taught by Professor Ragan during the Fall '08 term at McGill.

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2009 Midterm with - PHYS 131 MIDTERM October 26th 2009 WITH SOLUTIONS-The exam comprises two parts 6 short-answer questions and 4 problems

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