Two simple pendulums having lengths 144 cm and 121 cm starts executing oscillations. At some time, both bobs of the pendulum are at the equilibrium positions and in same phase. After how many oscillations of the shorter pendulum will both the bob’s pass through the equilibrium position and will have same phase?
$ T_1 = 2 \pi \sqrt { 144 \over g } and \,T_2 = 2 \pi \sqrt { 121 \over g } $ $ \therefore T_1 \gt T_2 $ When the shorter pendulum completes n oscillations, the longer one completes (n-1) oscillations (when in same phase). $ \therefore nT_2 = (n -1 ) T_1 $