Category: San Jose State University Plate Tectonics the Scientific Theory Lab Report

I’m studying for my Physics class and need an explanation .
PHYSICS 110 HOMEWORK # 6 Useful Information c = 3 . 0 x 108 m/s ! . ) ( a problem with ordinary non-relativistic velocities ) A boat whose speed in still water is 10km/hr is traveling along a river whose current is 4km/hr . (Take the direction of the current as the positive direction . ) a) What is the net speed of the boat when going downstream (with the current)? b) What is the net speed of the boat when going upstream (against the current)? 2 . ) ( a problem with relativistic velocities ) If you were on a space ship traveling at half the speed of light away from a bright star, at what speed would the star’s light go past you? (Note If you understand Relativity you do not have to do a calculation to answer this problem . Don’t do a calculation, just answer . ) 3 . ) ( The “”lifetime”” of an elementary particle is the time interval between the moment when the particle is created (“”birth””) and the moment when it “”decays”” into something else (“”death””) — in other words, it is the time during which the particle is “”alive”” . ) An elementary particle is traveling by you at a speed of 2 . 8 x 108 m/s . At this speed you measure its lifetime to be 2 . 5 x 10-8 s . a) What is the particle’s lifetime at rest? (For example, suppose you measure the particle’s lifetime when it is just sitting on your lab table and not moving . ) b) Does your answer show that the particle lives longer when it is at rest or when it is moving? 4 . ) (To measure astronomical distances such as the huge distances between stars, kilometers are inconveniently small . Instead it is conventional to measure large distances in terms of “”light-years”” (Ly) . A light-year is the distance light travels (at the speed of light in space) in one year . Note that a light-year is a distance, and not a time . One light-year is 1 Ly = c x t = (3 . 0 x 108 m/s) x 1 yr x (31 . 56 x 106 s/yr) = 9 . 47 x 1015 m . However, do NOT convert your answer to meters . It is much easier to understand if you leave it in light-years (Ly) in problems like this . If you convert to meters it will be assumed you did not read these instructions and just copied from something, and you will lose points . )a) If you were to travel to a star 50 light-years from Earth at a speed of 2 . 0 x 108 m/s what would you measure this distance to be? (Note that to you, in your space ship, it looks to you like you are standing still and the Earth-star distance is a moving length traveling by you . )b) As you travel, does your answer show that the distance to the star looks longer or shorter than the 50 light years seen from Earth?5 . ) (The “”rest mass”” of the electron is 9 . 11 x 10-31 kg . This is the mass the electron would have if it was sitting motionless on the lab table in front of you . )a) What is the mass of a moving electron traveling by you at v = 0 . 85 c ?b) Does your answer show the moving mass to be larger or smaller than the rest mass? 6 . ) Suppose that one could release all of the energy contained in a mass of 500 grams of dirt (0 . 500 kg, which is about a pound) . a) How much energy would be released (in Joules)?b) If the amount of energy released by burning one ton of coal is 22 billion Joules, how many tons of coal would you have to burn to equal the energy released by converting the mass of 500 grams (half of a pound) of dirt to energy? (note the energy released by burning coal is chemical energy, not rest mass energy . That is, the energy released by burning a mass, m, of coal is NOT = mc2 . You may treat 22 billion Joules/ton as a conversion factor as follows
N (tons of coal) x 22×109 J/ton = Energy released (from dirt) . “
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