phy121_f10_MT2-soln - Physics 121 Midterm 2. November 1,...

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Physics 121 Midterm 2. November 1, 2010 Exam form 0 1 This is a closed book exam. Use your own formula sheet, 8½ x 11 inches, double sided, handwritten. You may only use your own calculator; NO SHARING. ANY manipulation of electronic equipment (I-Pod, cell phone, laptop computer, pager, etc.) other than your calculator is strictly prohibited, and will result in a zero on this exam. Answer all problems on the bubble scan sheet. Before you start, enter your name and student ID number on the answer sheet . This is exam form 0. Mark 0 on the first digit of birth day on the bubble scan sheet . (Do not fill in your birth date.) There are twenty questions, each of which carries equal weight. Question 1: (1 point) A ski lift moves 3000 people up a1000 m mountain in one hour. Assuming the mass of a typical skier is 50 kg, how much power is required to run the ski lift? P = W/ t = F*d/ t = mgh/ t = (number of people)(mass/person)*g*h/ t = (3000)(50 kg)(9.81 m/s2)(1000m)/(3600s) = 409 kW Question 2: (1 point) Note: The work done by gravity is negative, mgsin Θ d, because gravity is working opposite the motion and tries to take energy away from the block, not add to it. Energy is not conserved because the speed is constant, so the person is adding energy to overcome gravity. A person pushes a block of mass m up a frictionless plane at a constant speed, exerting a force F push . Which of the following statements is correct? The work done by F push is W push = mg*sin Θ *d
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Physics 121 Midterm 2. November 1, 2010 Exam form 0 2 Question 3: (1 point) A ball of mass m B = 1kg with an initial velocity v is moving straight toward a stationary ball of mass 600 g. They collide in a head on elastic collision. After the collision, the ball with mass m B has velocity v’ = 4m/s. What was its initial velocity? For elastic, head on collisions we know v 1 ’ = (m 1 -m 2 )/(m 1 +m 2 )v 1 , so by doing algebra we find v1 = (m 1 +m 2 )/(m 1 -m 2 )v 1 ’ = 16 m/s. Question 4: (1 point) A beam of mass m B = 10. kg is held horizontal by a wire connected to the beam ¾ of the way to the end and making an angle φ =20 o with the beam. The beam is held to the wall by a frictionless hinge. What is the magnitude of the tension in the wire? This is an equilibrium problem, so use
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This note was uploaded on 03/06/2011 for the course PHY 121 taught by Professor Stephens during the Fall '08 term at SUNY Stony Brook.

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phy121_f10_MT2-soln - Physics 121 Midterm 2. November 1,...

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