Q: A plank of mass 12 kg is supported by two identical springs as shown in figure. The plank always remains horizontal. When the plank is pressed down and released, it performs simple harmonic motion with the period 3s. When a block of mass m is attached to the plank the time period changes to 6 s. The mass of the block is
(a) 48 kg
(b) 36 kg
(c) 24 kg
(d) 12 kg
Ans: (b)