# su08EI - Physics 53 Summer 2008 1 Exam I Solutions In...

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Unformatted text preview: Physics 53 Summer 2008 1 Exam I Solutions In questions or problems not requiring numerical answers, express the answers in terms of the symbols for the quantities given, and standard constants such as g . In numerical questions or problems, use g = 10 m/s 2 . Part A: Multiple choice questions. Check the best answer. Each question carries a value of 4 points. 1. Concerning the general principles of mechanics, which of the following is NOT a complete and correct statement? In an inertial frame, a body subject to no net force moves with constant velocity. The total force on an object is equal to the rate of change of its momentum. If body A exerts force F on body B, then body B also exerts force – F on body A. √ The change in total mechanical energy is equal to the work done by external forces. [Non-conservative forces, not external forces.] 2. A box is being pulled across a rough floor by application of a force F as shown. As the angle θ is increased, starting from zero, which of the following does NOT happen? The normal force exerted by the floor decreases. √ The kinetic friction force increases. [Decreases.] The horizontal component of F decreases. The acceleration of the box increases. θ F Physics 53 Summer 2008 2 3. A block slides all the way around the inside of a vertical circular track as shown. The track is frictionless. Points A, B, and C are at the top, side, and bottom of the track respectively. The minimum possible speed at A is zero. The speed is the same at all three points. The direction of the acceleration is toward the center of the circle at all three points. √ The total mechanical energy of the system is the same at all three points. [Only conservative forces do work.] 4. A mass m is attached to a vertical spring of stiffness k hanging from a ceiling as shown. Initially the mass is held a the height where the spring is at its equilibrium length. Which of the following is NOT true? If the mass is lowered slowly, it will hang at rest when the spring has been stretched through distance mg / k . If the mass is dropped from rest, it will stop momentarily after falling distance 2 mg / k . √ If the mass is dropped from rest, it will have its maximum acceleration when it has fallen distance mg / k . [Maximum speed at that point, zero acceleration.] If the mass is dropped from rest, it will return to its original height with zero instantaneous velocity. Part B: True-false questions. Mark each sentence with T of F. Each question has a value of 3 points. 1. In a head-on collision between a small car and a large SUV the acceleration of the two vehicles during the collision has the same magnitude. F [Forces have same magnitude (3 rd law) but masses are not equal.] 2. Curves on highways are banked to use a component of the normal force as part of the radial force, thus reducing the need for friction....
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## This note was uploaded on 10/19/2011 for the course PHYSICS 53L taught by Professor Mueller during the Spring '07 term at Duke.

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su08EI - Physics 53 Summer 2008 1 Exam I Solutions In...

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