Physics - SHM Question with Solution | TestHub

When a simple pendulum is in a lift accelerating upwards, the effective gravitational acceleration $g_{eff}$ is given by $g_{eff}=g+a$. Given that the upward acceleration $a=g/3$, we have $g_{eff}=g+\frac{g}{3}=\frac{4g}{3}$. The time period of a simple pendulum is $T=2\pi \sqrt{\frac{L}{g_{eff}}}$. Substituting the value of $g_{eff}$, the new time period $T^{\prime }=2\pi \sqrt{\frac{L}{4g/3}}=2\pi \sqrt{\frac{3L}{4g}}$.