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su09FinalS

# su09FinalS - Physics 53 Summer 2009 Final Exam Solutions In...

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Physics 53 Summer 2009 1 Final Exam Solutions In questions or problems not requiring numerical answers, express the answers in terms of the symbols given, and standard constants such as g . If numbers are required, use g = 10 m/s 2 . Part A: Multiple choice questions. Check the best answer. Each question carries a value of 4 points. 1. The total external force on a system is zero. It follows necessarily that: Total mechanical energy is conserved. Total linear momentum is conserved. Total angular momentum is conserved. All of these quantities are conserved. 2. In the situation shown, M > m , and the pulley has mass but no friction in its bearings. Which of the following is NOT true as the system moves? The tension in the left hand string is less than mg . [ T ! mg = ma > 0 .] The tensions in the two strings are different. The tension in the right hand string is less than Mg . Mechanical energy is conserved. 3. A platform diver leaves the platform rotating slowly forward, and then pulls her arms and legs tightly against her body while in the air. This reduces her moment of inertia about the axis of her rotation. Her rotation speed increases because: Energy is conserved. External torques produce an angular acceleration. Linear momentum is conserved. Angular momentum is conserved. m M

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Physics 53 Summer 2009 2 4. Three objects with the same mass roll without slipping from the same height down an incline as shown: a hoop of radius R , a solid sphere of radius R , and a solid sphere of radius 2 R . When they reach the bottom: The spheres have the same CM speed, which is less than that of the hoop. The spheres have the same CM speed, which is more than that of the hoop. [ K rot / K trans is greater for the hoop, and the same for both spheres.] The small sphere has the largest CM speed and the hoop has the smallest. All three have the same CM speed. 5. Two equal masses are executing SHM with the same frequency, but the amplitude of #1 is twice that of #2. The total energy of #1 is twice that of #2. [Four times.] The maximum acceleration of #1 is four times that of #2. [Twice.] The maximum speed of #1 is twice that of #2. None of the above is true. 6. A file card is resting on top of two paper clips on a table as shown. A jet of air can be directed into the page, either over or under the card. In either case the card will experience an upward force. In either case the card will experience a downward force. If the jet is directed over it the card experiences a downward force, but if the jet is directed under it the card experiences an upward force. If the jet is directed over it the card experiences an upward force, but if the jet is directed under it the card experiences a downward force. [Air in jet has lower pressure than in still air.] 7. When a metal rod of length L and cross section area A is placed between a hot and a cold object, the heat flow rate is 10 J/s. If the rod is cut in half and both pieces are placed between the same two objects, the net heat flow rate will be: 10 J/s.
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