55315737-11 - MasteringPhysics: Assignment Print View Page...

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MasteringPhysics: Assignment Print View Page 1 of 33 Homework 1 Due: 11:59pm on Sunday, September 12, 2010 Note: You will receive no credit for late submissions. To learn more, read your instructor's Grading Policy [Switch to Standard Assignment View] Converting Units The ability to convert from one system of units to another is important in physics. It is often impractical to measure quantities in the standard meters, kilograms, and seconds, but the laws of physics that you learn will involve constants that are defined in these units. Therefore, you may often have to convert your measured quantities into meters, kilograms, and seconds. The following table lists metric prefixes that come up frequently in physics. Learning these prefixes will help you in the various exercises. mega- ( kilo- ( ) centi- ( ) milli- ( ) ) micro- ( ) nano- ( ) When doing unit conversions, you need a relation between the two units. For instance, in converting from millimeters to meters, you need to know that . Once you know this, you need to divide one side by the other to obtain a ratio of . in the denominator, so that it will cancel the units of the If you are converting from millimeters to meters, then this is the proper ratio. It has , then you would have quantity that you are converting. For instance, if you were converting . If you were converting a quantity from meters to millimeters, you would use the reciprocal ratio: . to : Part A Suppose that you measure a pen to be 10.5 Hint A.1 long. Convert this to meters. Relating centimeters and meters Hint not displayed Express your answer in meters. ANSWER: 10.5 = 0.105 Correct When converting areas, you must be careful to use the correct ratio. If you were converting from to , it might be tempting to use again. Be careful! Think of as . That is to say, think of this as a pair of millimeter units, each of which must be to square meters you would use the following calculation: . converted separately. To convert Notice that the exponent distributes to both the numbers and the units: . Now the will cancel properly: . http://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=1425767 9/16/2010
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MasteringPhysics: Assignment Print View Page 2 of 33 Part B Suppose that, from measurements in a microscope, you determine that a certain bacterium covers an area of meters. Hint B.1 Find the conversion factor Hint not displayed . Convert this to square Express your answer in square meters. ANSWER: 1.50 = 1.50×10−12 Correct As with areas, you must be careful when converting between volumes. For volumes, you must cancel off three copies of whatever unit you are converting from. Part C Suppose that you find the volume of all the oceans to be in a reference book. To find the mass, you can use the density of water, also found in this reference book, but first you must convert the volume to cubic meters. What is this volume in cubic meters? Hint C.1 Find the conversion factor Hint not displayed Express your answer in cubic meters. ANSWER: = 1.40×1018 Correct
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55315737-11 - MasteringPhysics: Assignment Print View Page...

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