A uniform chain of 6 m length is placed on a table such that a part of its length is hanging over the edge of the table. The system is at rest. The co-efficient of static friction between the chain and the surface of the table is 0.5, the maximum length of the chain hanging from the table is ___________ m.

A 0.5 kg block moving at a speed of 12 ms^$$-$$1 compresses a spring through a distance 30 cm when its speed is halved. The spring constant of the spring will be _______________ Nm^$$-$$1.

The velocity of upper layer of water in a river is 36 kmh^$$-$$1. Shearing stress between horizontal layers of water is 10^$$-$$3 Nm^$$-$$2. Depth of the river is __________ m. (Co-efficient of viscosity of water is 10^$$-$$2 Pa.s)

The first overtone frequency of an open organ pipe is equal to the fundamental frequency of a closed organ pipe. If the length of the closed organ pipe is 20 cm. The length of the open organ pipe is _____________ cm.