Answer:[tex]d=7.94\times 10^5\ m[/tex]
Explanation:
Given
Speed of Primary wave [tex]v_1=8\ km/s[/tex]
Speed of secondary wave [tex]v_2=4.5\ km/s[/tex]
difference in timing of two waves are [tex]77.2\ s[/tex]
Suppose both travel a distance of d km then
[tex]t_1=\frac{d}{8}\quad \ldots (i)[/tex]
[tex]t_2=\frac{d}{4.5}\quad \ldots (ii)[/tex]
Subtract (ii) from (i)
[tex]\frac{d}{4.5}-\frac{d}{8}=77.2[/tex]
[tex]d[\frac{1}{4.5}-\frac{1}{8}]=77.2[/tex]
[tex]d[0.0972]=77.2[/tex]
[tex]d=794.23\ km[/tex]
[tex]d=7.94\times 10^5\ m[/tex]
