The time period of oscillation of a simple pendulum of length \( L \) suspended from the roof of a vehicle, which moves without friction down an inclined plane of inclination \( \alpha \), is given by:
\( 2\pi \sqrt{ {L}/({g \cos \alpha}) } \)
\( 2\pi \sqrt{ {L}/({g \sin \alpha}) } \)
\( 2\pi \sqrt{ {L}/{g} } \)
\( 2\pi \sqrt{ {L}({g \tan \alpha}) } \)