Question

The escape velocity from an altitude equal to radius of the Earth above Earth's surface is:
$($ Escape velocity from surface of the Earth is $11.2$ kms${}^{-1}$ $)$

• A. $5.6$ kms${}^{-1}$
• B. $7.92$ kms${}^{-1}$
• C. $2.8k$ ms${}^{-1}$
• D. $11.2$ kms${}^{-1}$

Answer 1

Answer: (B)

$7.92$ kms${}^{-1}$

Escape speed is $v_e=\sqrt{\frac{2GM}{R}}=11.2$ km/s on Earth's surface.
Escape speed from an altitude $R$ from Earth's surface that is $2R$ distance from the centre of Earth, is
$v_e^{{}^{\prime }}=\sqrt{\frac{2GM}{2R}}=11.2\times \frac{1}{\sqrt{2}}=7.919$ km/s