Question

The escape velocity from the earth is about . The escape velocity from a planet having twice the radius and the same mean density as the earth, is

• A. 22 km/s
• B. 11 km/s
• C. 5.5 km/s
• D. 15.5 km/s

Answer 1

Answer: (A)

22 km/s

Answer 2

$v _ { e } = \sqrt { \frac { 2 G m } { R } } = \sqrt { \frac { 8 } { 3 } \pi \rho G R ^ { 2 } }$ $\therefore v _ { e } \propto R$ if $\rho$= constant. Since the planet having double radius in comparison to earth therefore the escape velocity becomes twice i.e. $22 \mathrm {~km} / \mathrm { s }$ .