$\"\"$

The force between the masses $\"\"$ and $\"\"$ : $\"\"$ .

Find the instantaneous rate of change of $\"\"$ with respect to $\"\"$ .

$\"\"$

Apply derivative on each side with respect to $\"\"$ .

$\"\"$

$\"\"$ .

Instantaneous rate of change of $\"\"$ with respect to $\"\"$ is $\"\"$ .