Question

Figure shows a bob of mass $m$ suspended from a string of length $L$. The velocity is $V _0$ at $A$, then the potential energy of the system is _______at the lowest point $A$.

• A. $\frac{1}{2} m v_0^2$
• B. $mgh$
• C. $\frac{-1}{2} mv _0^2$
• D. zero

Answer 1

Answer: (D)

At the lowest point, $h =0$
$ \therefore$ P.E. $=0$ (gravitational P.E.). There is no work done on the bob by the tension as it is perpendicular to the displacement.
$\therefore$ Potential energy is associated only to the gravitational force.