Question

There are two isolated stars orbiting each other. The first star has a mass of $2\times {10}^{12}kg$ and the second star has a mass of $4.5\times {10}^{14}kg$. If the stars are 2,000km away, what is the gravitational force felt by the first star?
$G=6.67\times {10}^{–11}{m}^{3}kgs$

• A. $1.5\times {10}^{9}N$
• B. 0 N
• C. $1.5\times {10}^{14}$
• D. $1.5\times {10}^4$

Answer 1

The correct option is D $1.5\times {10}^4$

By newton’s laws of gravitation we have
$F=G\frac{m_1{m}_2}{r^2}$
Both the stars feel the same force. Therefore,
$F=G\times \frac{2\times {10}^{12}kg\times 4.5\times {10}^{14}}{(2\times {10}^6{)}^2}$
G = $6.67\times {10}^{-11}$
$m_1=2\times {10}^{12}kg$
$m_2=4.5\times {10}^{14}kg$
$r=2\times {10}^{6}m$
$F=1.5\times {10}^{4}N$
Therefore, option D is correct.