Question

2 simple pendulums of length l and 16 l are released from same phase together . after what minimum time will be they together

Answer 1

T =√(l/g)  × 2π

T'=√(16l/g) × 2π = 8π  *√(l/g) = 4T.

they will be together when the slowest pendulum reaches it's mean position for the first time. 
 at t/4 the will be togeather.