Correct Answer - C
Since the pendulum started with no kinetic energy, conservation of energy implies that the potential energy at `Q_(max)` must be equal to the original potential energy, i.e., the vertical position will be same. Therefore,
`Lcos alpha=l+(L-l)cos theta`
`implies cos theta=(Lcos alpha-1)/(L-1)`
`impliestheta=cos^-1[(Lcos alpha-1)/(L-1)]`