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# Answ1 - PHY 341 Quiz 1 Answer Key 1 I Three Quickies 1...

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PHY 341 Quiz 1 Answer Key 1 I) Three Quickies 1.) Evaluate g , the acceleration due to gravity at the earth’s surface, in “Star Trek” units where time is measured in years and distance in light-years. Let T be the number of seconds per year. T π × 10 7 s / yr. g 10 m / s 2 × T 2 / ( c × T ) = gT/c . Therefore, g 1 lt · yr / yr 2 ! So-called “natural units” of measure can be derived from various physical quantities by combining the quantity with powers of the speed of light c (SI units: m / s) and Planck’s constant h (SI units: J · s) to achieve the desired unit of measure. Suppose we choose the mass m of some particle as the standard of a system of natural units. Then, for example, the unit of energy is mc 2 . 2.) What will be the unit of length in such a system of natural units? mc 2 /h will have units of [ energy] / [ energy · t] = [ t 1 ]. This collection needs to be divided by c to have units of [ L 1 ]. Hence, the combination h/mc will have units of length. 3.) Estimate the number of barber shops in Austin, giving your reason- ing. Take the population of Austin to be 1 million. There are approximately 10 6 people needing a haircut every four weeks. A given shop has about 4 or 5 people giving a hair- cut in about 1/2 to 1 hour.

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