Phys298Exam3Sp08-Solution

Phys298Exam3Sp08-Solution - Phys 298 Brown Friday, April...

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Phys 298 Brown Exam 3 Name _____________________________ Friday, April 11, 2008 This is a closed-book, closed-note, closed-neighbor exam. You are allowed one 3”x5” card with information, a calculator (not a computer), and your writing instruments. Multiple choice questions each have only one correct choice. Partial credit will be given on the ‘work-out’ problems. You may use the value g = 10 m/s 2 where needed. Good luck, and “May the Net Force be with you!” 1. An irregularly shaped planar object as shown has mass m distributed with uniform density. The distance from the object’s center of mass to the most distant point on the object is L . The moment of inertia for this object about its center of mass is: a. Equal to ½ mL 2 b. Equal to mL 2 c. Less than mL 2 d. Greater than mL 2 e. Not enough information given 2. A disk of radius 2 cm and mass 0.25 kg, a solid cylinder of radius 2 cm and mass 0.75 kg, a disk of radius 5 cm and mass 1.0 kg, and a solid cylinder of radius 5 cm and mass 1.8 kg all race starting from rest at the top of an incline. Which one wins the race? a. The disk of radius 2 cm b. The cylinder of radius 2 cm c. The disk of radius 5 cm d. The cylinder of radius 5 cm e. It’s a 4-way tie 3. You can use a simple harmonic oscillator to keep time. Which of these would work best as a time-keeper if you traveled through space as an astronaut? a. A mass on a spring b. A physical pendulum c. A simple pendulum d. The ‘scat’ singing style of Ella Fitzgerald e. The frequency with which your astronaut kids say, “Are we at the Moon yet?” If it were a single point mass a distance L from the axis, it would be mL 2 . But much of this mass is less than the distance L from the axis so I is less than this. mgh = ½ mv 2 + ½ Iw 2 mgh = ½ mv 2 + ½ ( ½ mR 2 )(v/R) 2 gh = ½ v 2 (1+ ½ ) Notice that the mass and radius both cancel. All that matters is that factor of
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Phys298Exam3Sp08-Solution - Phys 298 Brown Friday, April...

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