Just before getting taut, speed of m is V1 = √2g×2l = 2 √gl Just after getting taut let the velocity of m be V2 (downwards) and so velocity of 2m will be V2 (upwards) upwards is taken as + ve. For m1 l = (−mV2) - (-mV1) = mV1 - mV2 For 2m1 l = (2mV2) - (0) = 2mV2 ∴ mV1 - mV2 = 2mV2 ⇒ V2 =