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Unformatted text preview: huynh (hph268) HW #5 clark (56485) 1 This print-out should have 19 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points If a spring with a spring constant k = 10 N / m is stretched from its equilibrium position by . 1 m , and released, what would be the maxi- mum kinetic energy at any time in its motion? Neglect friction. 1. 0.1 J 2. 0.05 J correct 3. 0.025 J 4. 1 J 5. Not enough information given Explanation: The maximum kinetic energy is equal to the potential energy stored in the spring at maximum displacement from equilibrium: K = U = 1 2 k x 2 = 1 2 (10 N / m)(0 . 1 m) 2 = . 05 J . 002 10.0 points Use the potential energy vs . position plot shown below to answer the following question. A particle is released from point A and moves in the potential U ( x ). Suppose the mechanical energy of the system is conserved. x U ( x ) T Y V A At which position(s) will the kinetic energy of the particle have its maximum value? 1. Points T and V . 2. Point Y . 3. Point T . correct 4. Point V . 5. The particle remains stationary at point A . Explanation: Since the total energy is constant, the max- imum kinetic energy will occur when the po- tential energy is a minimum. The ball will never reach Y . Thus point T is the correct answer. 003 10.0 points A lunar vehicle is tested on Earth at a speed of 10 km/h. When it travels this fast on the moon, how does its momentum compare to the momen- tum on Earth? 1. None of these 2. less than on Earth 3. the same as on Earth correct 4. greater than on Earth Explanation: Its momentum is m v . Because its mass and speed do not change, its momentum on the moon is the same as that on Earth. 004 10.0 points Suppose the entire population of the Earth gathers at one spot and, at the sound of a pre- arranged signal, everyone jumps up. About a second later, 5 billion people land back on the ground. After the people have landed, Earths mo- mentum is 1. the same as what it was before the people jumped. correct huynh (hph268) HW #5 clark (56485) 2 2. different from what it was before the peo- ple jumped. Explanation: It is impossible to change the momentum of an isolated system from inside the system. 005 10.0 points An open train car moves with speed 16 . 2 m / s on a flat frictionless railroad track, with no engine pulling the car. It begins to rain. The rain falls straight down and begins to fill the train car. The speed of the car 1. decreases. correct 2. stays the same. 3. increases. Explanation: Using Newtons second law, we have dP dt = 0 , since no external forces act on the train in the horizontal direction. With no rain, the train will move at a constant velocity; however, when it starts to rain and the rain starts to fill the car, the mass of the train changes....
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