Question

The potential energy U between two molecules as a function of the distance X between then has been shown in the figure. The two molecules are

• A. Attracted when x lies between A and B and are repelled when X lies between B and C
• B. Attracted when x lies between B and C and are repelled when X lies between A and B
• C. Attracted when they reach B
• D. Repelled when they reach B

Answer 1

Answer: (B)

Attracted when x lies between B and C and are repelled when X lies between A and B

$F=-(\frac{dU}{dx})$.
In the region $BC$ slope of the graph is positive
$\therefore F=\text{negative}$ i.e. force is attractive in nature
In the region $AB$ slope of the graph is negative
$\therefore F=\text{positive}$ i.e. force is repulsive in nature