Teaching Modern Physics - QuarkNet - Fermilab
Teaching Modern Physics - QuarkNet - Fermilab
Teaching Modern Physics - QuarkNet - Fermilab
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<strong>Modern</strong> <strong>Physics</strong><br />
Relativity Homework Set #2<br />
1. Imagine an astronaut on a trip to Sirius, which is eight light-years from Earth. On arrival at<br />
Sirius, the astronaut finds that the trip lasted six years. If the trip was made at a constant<br />
speed of 0.8 c, how can the eight light-year distance be reconciled with the six-year duration?<br />
2. Some distant star-like objects, called quasars, are receding from us at half the speed of light<br />
or greater. What is the speed of light we receive from these quasars? Explain.<br />
3a. An unstable high-energy particle enters a detector and leaves a track 1.05 mm long before it<br />
decays. Its speed relative to the detector was 0.992 c. What is its proper lifetime? That is,<br />
how long would the particle have lasted before its decay in its own reference frame (at rest<br />
relative to the detector)?<br />
b. A pi-meson has an average lifetime in its own frame of reference of 2.6 x 10 -8 seconds.<br />
(This is the proper lifetime.) If the meson moves with a speed of 0.95 c, what is its mean<br />
lifetime as measured by an outside observer,<br />
c. And the average distance it travels before decaying?<br />
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