Question

 A star is 5.00 ly from the Earth. At what speed must a spacecraft travel on its journey to the star such that the Earth–star distance measured in the frame of the spacecraft is 2.00 ly

Answer 1

Explanations & Calculations

$\qquad\qquad \begin{aligned} \small \Delta L&=\small \gamma \Delta L_0\\ \small 5&=\small \frac{1}{\sqrt{1-\large\frac{v^2}{C^2}}}\times2\\ \small v&=\small 0.917C \end{aligned}$