Question

Potential energy for a pair of nucleons versus separation between the nucleons is plotted below.

Match the following columns.

Column I		Column II
A	Force between nucleons is zero.	1	$r > 0.8\, fm$
B	Force between nucleons is attractive.	2	$r < 0.8\, fm$
C	Force between nucleons is repulsive.	3	$r=0.8\, fm$
D	Potential energy is minimum.	4	$r=0$

• A. A-(3), B-(1), C-(2), D-(4)
• B. A-(3), B-(2), C-(1), D-(4)
• C. A-(4), B-(3), C-(2), D-(1)
• D. A-(3), B-(1), C-(2), D-(3)

Answer 1

Answer: (D)

A rough plot of the potential energy between two nucleons as a function of distance shows that the potential energy is a minimum at a distance $r_{0}$ of about $0.8\, fm$.
This means that the force is attractive for distances larger than $0.8\, fm$ and repulsive if they are separated by distances less than $0.8\, fm$.