The critical speed of satellite orbiting close to the earth’s surface is,

Explanation

For a satellite orbiting very close to the surface of earth, the critical speed`V_c=sqrt((GM)/R)`but `GM=gR^2
V_c=sqrt((gR^2)/R)=sqrt(gR)`
`sqrt(10xx6.4xx10^6)=sqrt(64xx10^6)=8xx10^3 m//s`