Answer:
The speed of Lilac is 0.422 times of the speed of light.
Explanation:
Given that,
Length of the spaceship Lilac at rest, [tex]L_o=759\ m[/tex]
When Lilac passes Earth, observers there measure its length to be 688 m, L = 688 m
We need to find the speed of light is Lilac moving with respect to Earth. The formula of length contraction is given by :
[tex]L=L_o\sqrt{1-\dfrac{v^2}{c^2}} \\\\\dfrac{v}{c}=\sqrt{1-(\dfrac{L}{L_o})^2} \\\\\dfrac{v}{c}=\sqrt{1-(\dfrac{688}{759})^2} \\\\\dfrac{v}{c}=0.422\\\\v=0.422c[/tex]
So, the speed of Lilac is 0.422 times of the speed of light.