Time period of revolution is T2=4π2GMr3
⇒T21T22=r31r32
Given T1=1 hr, T2=2 hr and r1=104 km.
⇒r2=r1×T2/32T2/31=104×82/312/3=4×104 km
Now,
v1=r1ω1=r12πT1=104×2π1=2π×104 km/hr ( since we want the answer in kmph, we didn't convert km to m and hr to s while substituting )
v2=r2ω2=r22πT2=4×104×2π8=π×104 km/hr
Since we want the relative speed when the satellites are closer, direction of linear speed is in the same direction.
Hence, relative speed=(v1−v2)=(2π−π)×104=π×104 km/hr