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Example Problems for Ch. 37 Part 1 Problem 37.7
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Problem 37.7 A spacecraft flies away from the earth with a speed of 4.80 x 106 m/s relative to the earth and then returns to the earth at the same speed. The space craft returns to the earth 365 days later as measured by an atomic clock on the earth. If there is an atomic clock on the spaceship which was previously synchronized to the clock on the earth, what is the difference in elapsed times as measured by the two clocks? Which clock shows the smallest elapsed time?
Convert to fraction of c • This is the easiest way to deal with the radical sign. • 4.80 x 106 m/s / 3 x 108 m/s is 0.016 so • v=1.6%c
This is a time dilation problem • In our case, we must determine which clock measures proper time • The clock is at rest on the moving spaceship • So Dt=365 days • So now solve for Dt0 using u=1.6%c
Substituting • So Dt=365 days • So now solve for Dt0 using u=1.6%c
Problem 37.13 A space craft of the Trade Federation flies past the planet Coruscant at a speed of 0.600c. A scientist on Coruscant measures the length of the moving space craft to be 74 m. The spacecraft later lands on Coruscant and the scientist now measures the length of the now stationary spacecraft. What value does she get?
This is a length contraction problem • L0 is the proper length • L=74 m • u=0.6c
Problem 37.23 An imperial spaceship moving at high speed relative to planet Arrakis, fires a rocket toward the planet with a speed of 0.920c relative to the spaceship. An observer on Arrakis measures that the rocket is approaching with a speed of 0.36c. • What is the speed of the spaceship relative to Arrakis? • Is the spaceship moving towards or away from Arrakis?
Draw It! vx=0.36c u vx’=0.92c Arrakis
Must solve for velocity, u Since u<0, spaceship moving away