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The identical twins Speedo and Goslo join a migration from the Earth to Planet X, 20.0 ly away in a reference frame in which both planets are at rest. The twins, of the same age, depart at the same moment on different spacecraft. Speedo’s spacecraft travels steadily at 0.950c and Goslo’s at 0.750c. Which twin is older?
A source of red light has a higher power than a source of green light. (a) Is the energy of the photons emitted by the red source greater than, less than, or equal to the energy of the photons emitted by the green source? (b) Choose the best explanation from among the following: A. The photons emitted by the red source have greater energy because that source has the greater power. B. The photons from the red source have less energy than the photons from the green source because they have a lower frequency. The power of the source doesn't matter. C. Photons from the red source have a lower frequency, but that source also has the greater power. The two effects cancel, so the photons have equal energy.