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Unformatted text preview: MasteringPhysics http://session.masteringphysics.com/cgibin/CT.pl?teacherProblemVi... 1 of 3 10/29/2004 08:56 AM Options: show answer statistics report wrong answers submit Note: selecting options may require report generation times of several minutes for large classes Problem Solution/Report Part 1: Mechanics Chapter 1: Units, Physical Quantities, and Vectors Problem Title: Converting Units: The Magic of 1 Problem Description: Explains method to convert units, then has several examples, the hardest being velocity Learning Goal: To learn how to change units of physical quantities. Quantities with physical dimensions like length or time must be measured with respect to a unit , a standard for quantities with this dimension. For example, length can be measured in units of meters or feet, time in seconds or years, and velocity in meters per second. When solving problems in physics, it is necessary to use a consistent system of units such as the International System (abbreviated SI, for the French Système International) or the more cumbersome English system. In the SI system, which is the preferred system in physics, mass is measured in kilograms, time in seconds, and length in meters. The necessity of using consistent units in a problem often forces you to convert some units from the given system into the system that you want to use for the problem. The key to unit conversion is to multiply (or divide) by a ratio of different units that equals one. This works because multiplying any quantity by one doesn’t change it. To illustrate with length, if you know that , you can write . To convert inches to centimeters, you can multiply the number of inches times this fraction (since it equals one), cancel the inch unit in the denominator with the inch unit in the given length, and come up with a value for the length in centimeters. To convert centimeters to inches, you can divide by this ratio and cancel the centimeters. Part A. How many centimeters are there in a length 842.3 ? Express your answer in centimeters to three significant figures. 2.54*l_1 (+/ 0.3%) Numeric Solution: 2139 Sometimes you will need to change units twice to get the final unit that you want. Suppose that you know how to convert from centimeters to inches and from inches to feet. By doing both, in order, you can convert from centimeters to feet. Part B. Suppose that a particular artillery piece has a range 1.244×10 4 . Find its range in miles. Use the facts that and . Part 1. The first step in this problem is to convert from yards to feet, because you know how to then convert feet into miles. MasteringPhysics http://session.masteringphysics.com/cgibin/CT.pl?teacherProblemVi... 2 of 3 10/29/2004 08:56 AM Convert 1.244×10 4 into feet. Use ....
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 Winter '08
 JohnEllison
 Physics, Acceleration, Velocity, International System of Units, Archimedes

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