Question

The mass of a spaceship is $1000kg$. It is to be launched from the earths surface out into free space. The value of $g$ and $R$ (radius of earth) are $10m/s$ and $6400km$ respectively. The required energy for this work will be :

• A. $6.4\times {10}^{8}J$
• B. $6.4\times {10}^{11}J$
• C. $6.4\times {10}^{9}J$
• D. $6.4\times {10}^{10}J$

Answer 1

Answer: (D)

$W=\frac{GMm}{r}$
$=g{R}^2\times \frac{m}{R}=mgR$
$=1000\times 10\times 6400\times {10}^3$

$=6.4\times {10}^{10}$