- Spacecraft S leaves Earth with speed 0.60c on the way to a planet P. As measured by Earth, P is at a distance of 30 ly from Earth. The diagram shows the spacetime axes of Earth (x, ct) and of S (x′, ct′).
(a) S arrives at P after 50 years according to Earth. Calculate the time at which S arrives at P according to S clocks. [2]
(b) When S arrives at P, S sends a radio signal back to Earth.
(i) Draw, on the spacetime diagram, the world line of the signal from when it is emitted until it is received on Earth. [1]
(ii) Determine, using the spacetime diagram or otherwise, the time of travel of the signal according to S. [3]