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UW-Madison PHYSICS 207 - Phy 207 Exam 3

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1 First Name: __________________Last Name: _________________ Section: ______ 3 December, 2009 Physics 207 EXAM 3 Please print your name and section number (or TA’s name) clearly on the first page. Show all your work in the space immediately below each problem. Your final answer must be placed in the boxes, when provided. Problems will be graded on reasoning and intermediate steps as well as on the final answer. Be sure to include units wherever necessary, the direction of vectors, and the correct number of significant figures. Check your answers to see that they have the correct dimensions (units) and are the right order of magnitude. You are allowed 1 side of 1 sheet of notes (8.5” x 11”, 1 side), a calculator, and the constants in this exam booklet. Each part is worth 20 points. Try to be neat! The exam lasts 1.25 hours. Constants and Conversion Factors: Acceleration due to gravity at Earth’s surface: g = 9.81 m/s2 1.0 km = 0.62 miles 1 atm =101,000 Pa 1 hp = 746 W moment of inertial, I, for a solid disk of mass M and radius R = MR2/2 SCORE: Problem 1: __________ Problem 2: __________ Problem 3: __________ Problem 4: __________ Problem 5: __________ TOTAL: ___________ Please don't open the exam until you are instructed to start.2 Part 1 A. A particular motor can provide a maximum of 110 N•m of torque. Assuming that all of this torque is used to accelerate a solid, uniform flywheel of mass 10.0 kg and radius 3.0 m, how long will it take for the flywheel to accelerate from rest to 6.0 rad/s? (Note - the moment of inertial for a solid disk of mass M and radius R is I = MR2/2.) (10 pts) B. An irregularly shaped object 10 m long is placed with each end on a scale. If the scale on the right reads 74 N and the scale on the left reads 93 N how far from the left is the center of gravity? (10 pts)3 Part 2 A. A 2.0 kg block on a frictionless table is connected to two springs with spring constants k1 and k2 whose opposite ends are fixed to walls, as show in the figure. What is the oscillation angular frequency if k1= 7.6 N/m and k2 = 5.0 N/m? (10 pts) B. A mass on a spring has an angular oscillation frequency of 2.8 rad/s. The mass has a maximum displacement (when t = 0 s) of 0.23 m. If the spring constant is 46 N/m, what is the potential energy stored in the mass-spring system when t = 1.4 s? (10 pts)4 Part 3 A. High winds caused by tornadoes can destroy houses by creating large pressure differences between the inside and outside of a structure. Suppose air is flowing across the flat, horizontal roof of a house at 200 km/hr. Assume the pressure inside the building is 1 atm. (i) What is the pressure outside the house, just above the roof? (5 pts) (ii) Suppose the roof has an area of 100 m2. What is the force (magnitude and direction) exerted on the roof by the pressure difference? (5 pts) B. A spherical ball of lead (density 11.3 g/cm3) is placed in a tub of mercury (density 13.6 g/cm3). Which answer best describes the result? Show your calculations. (10 pts) i) The lead ball will float with about 83% of its volume above the surface of the mercury. ii) The lead ball will float with its top exactly even with the surface of the mercury. iii) The lead ball will float with about 17% of its volume above the surface of the mercury. iv) The lead will sink to the bottom of the tub.5 Part 4 A. Pluto's average distance from the sun is 5.9 x 1012 m. Calculate the Sun's intensity at the distance of Pluto, assuming the sun radiates a total power of 4.0 x 1026 W. (10 pts) B. A standing wave is oscillating at 690 Hz on a string, as shown in the figure. What is the wave speed? (10 pts)6 Part 5 A. Find the speed of an ocean wave whose displacement is given by y = 3.7 cos(2.2x – 5.6t) where x and y are in meters and t is in seconds. (10 pts) B. A plucked guitar string produces a sound wave of frequency 440 Hz. (i) What is the wavelength of the sound wave (assume the speed of sound in air is 340 m/s)? ( 5pts) (ii) How much time elapses between the impacts of two adjacent compressions on your eardrum? (5


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UW-Madison PHYSICS 207 - Phy 207 Exam 3

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Syllabus

Syllabus

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Lecture 3

Lecture 3

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Lecture 3

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Lecture 8

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Lecture 1

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Lecture 5

Lecture 5

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Lecture 5

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Lecture26

Lecture26

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