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su09EIS - Physics 53 Summer 2009 Exam I Solutions Part A...

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Physics 53 Summer 2009 1 Exam I Solutions Part A: Multiple choice questions. Check the best answer. 1. The total mechanical energy of a particle: Always decreases if non-conservative forces do work. [Can increase] Is always positive. Changes by the total amount of work done by all forces. [Only non- conservative forces] Is constant if only conservative forces do work. 2. Shown are trajectories for three projectiles launched with the same initial speed. Which of the following is NOT true? #1 reaches its target in the least time. #3 stays in flight the longest. The elevation angles at launch for #1 and #2 add to 90°. A projectile launched at an angle between those of #1 and #2 will not go as far as either of those. [Farther] 1 2 3
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Physics 53 Summer 2009 2 3. In the situation shown, a block is being dragged across a rough floor by pulling on the rope with force T . The coefficient of kinetic friction is μ k . The force of friction on the block has magnitude: μ k mg μ k T sin ! μ k ( mg ! T sin " ) Cannot be determined without knowing the block’s acceleration. 4. The total potential energy for a combination of conservative forces is given by U ( x ) = x 2 ! 2 x . Which of the following is NOT true? The system has only one point of static equilibrium, at x = 1 . The formula for the total force is F x = 2 ! 2 x . The equilibrium at x = 1 is unstable. [Stable] If the total energy is zero, there are turning points at x = 0 and x = 2 . Part B: True-false questions. Mark each sentence with T of F. Each question has a value of 3 points. 1. The purpose of a simple machine (such as an inclined plane or a lever) is to do the same work with a smaller force over a larger distance.
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