Express escape velocity in terms of g, R and `rho` (the earth's density).

Explanation

Escape velocity, `v_("esc")=sqrt((2GM)/(R))`
The earth's density, `rho=("mass")/("volume")=(M)/(((4)/(3))piR^(3))`
`therefore M=(4)/(3)piR^(3)rho`
`therefore v_("esc")=sqrt((2G(4//3)piR^(3)rho)/(R))`
`=sqrt(2G(4//3)piR^(2)rho)=2R sqrt(((2)/(3)Gpi rho)`