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CHECK YOURSELF ANSWERS
1B and C because there is no acceleration.
29 m sâ1 due south.
3No, we have to subtract the time it took light to get to the observer.
4If A and B are separated by a distance Îx, the time it would take the photon to get to B would be Îxc. The spacetime interval is then c2(Ît)2â(Îx)2=c2(Îx)2c2â(Îx)2=0.
5aYes
bYes
cNo
6The spacetime diagram in Figure 6.47 shows that the left tree was hit first. Photon lines from the strikes arrive at the rocket at the same time.
7In frame S the light will reach the spacecraft in a time t given by 0.6ct + ct = 4 â ct = 2.5 ly when the spacecraft is at x=0.6cÃ2.5c=1.5Â ly. The gamma factor is 1.25 and so ctâ²=1.25Ã(2.5â0.6ccÃ1.5)=2.0Â ly.

Figure 6.47: For check yourself question 6.

