Question

A simple pendulum is released from $A$ as shown in figure. If $m$ and $l$ represent the mass of the bob and the length of the pendulum respectively, the gain in kinetic energy at $B$ is then

• A. $\frac{mgl}{2}$
• B. $\frac{mgl}{\sqrt{2}}$
• C. $\frac{\sqrt{3}}{2}mgl$
• D. $\frac{2}{\sqrt{3}}mgl$

Answer 1

The correct option is C $\frac{\sqrt{3}}{2}mgl$

Initial energy $=mgl$

But, as per the given in question,

$PE=0$

gain in $KE=mgl\cos 30$

$KE=mgl\frac{\sqrt{3}}{2}$

$\therefore$ option C is the correct solution