Question

Two spheres each of mass ${10}^{5}kg$ and radius $10m$ are kept in contact. Find the gravitational force acting between them.

• A. ${10}^{-3}N$
• B. $1.67\times {10}^{-3}N$
• C. $6.67\times {10}^{-11}N$
• D. ${10}^{-11}N$

Answer 1

The correct option is B $1.67\times {10}^{-3}N$

$M_1=M_2={10}^{5}kgR=10m$

Clearly $r$ is the distance between their centres which is equal to sum of their radii

$Hencer=2R=2\times 10=20m\therefore F=\frac{G{M}_1{M}_2}{{\left(r\right)}^2}=\frac{G{M}_1{M}_2}{{\left(2R\right)}^2}=\frac{6.67\times {10}^5\times {10}^5\times {10}^{-11}}{{20}^2}=1.66\times {10}^{-3}N$