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Unformatted text preview: b) PHY28  HE N9. 2 . One of the strongest emission lines observed from distant galaxies comes from hydrogen and has a wavelength of 122 nm (as measured in the restframe of the light
source). How fast must a galaxy be moving away from us in order for that line to be observed
in the visible region at 366 nm? What would be the wavelength of the line if that galaxy were moving toward us at the
same speed? Observer O sees a red ﬂash of light at the origin at t:0 and a blue ﬂash of light at
x=3.26 km at a time t=7.63 us. What are the distance and the time interval between the ﬂashes according to observer 0', who moves relative to O in the direction of
increasing x with a speed of 0.625c? Assume that the origins of the two coordinate systems line up at t=t':0. . Suppose rocket traveler Amelia has a clock made on Earth. Every year on her birthday she sends a light signal to brother Casper on Earth. (Use the quantities given
in Section 2.6 of your textbook). At what rate does Casper receive the signals during Amelia's outward journey? At what rate does he receive the signals during her return journey? How many of Amelia's birthday signals d0es Casper receive during the journey that
he measures to last 40 years? Use the binomial expansion
(l+x)“=1+nx+[n(n—1)/2!]x2+. .. to show that the expression for the relativistic kinetic energy reduces to the classical
form (1/2)mv2 when v<<c. By evaluating the first term in the expansion beyond
(1/2)mv2, find the speed necessary before the classical expression is off by 0.01
percent. ’ . An electron and a proton (the rest energies are given in your textbook) are each accelerated through a potential difference of 10.0 million volts. Find the momentum
(in MeV/c) and the kinetic energy (in MeV) of each. Compare with the results of
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 Spring '10
 MetCalfe
 Kinetic Energy, Amelia, strongest emission lines, rocket traveler Amelia, birthday signals d0es

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