An annular disc has a mass m, inner radius R and outer radius $$2R$$. The disc rolls on a flat surface without slipping. If the velocity of the center of mass is $$v,$$ the kinetic energy of the disc is

A mass m₁ of 100kg travelling with a uniform velocity of 5 m/s along a line collides with a stationary mass m₂ of 1000kg. After the collision, both the masses travel together with the same velocity. The coefficient of restitution is

A fluid of dynamic viscosity $$2 \times {10^{ - 5}}\,\,kg/m.s$$ and density $$1kg/{m^3}$$ flows with an average velocity of $$1$$ $$m/s$$ through a long duct of rectangular $$\left( {25\,\,mm \times \,\,15\,\,mm} \right)$$ cross-section. Assuming laminar flow, the pressure drop (in $$Pa$$) in the fully developed region per meter length of the duct is __________________.

Consider the turbulent flow of a fluid through a circular pipe of diameter, $$D.$$ Identify the correct pair of statements.
$${\rm I}.$$ The fluid is well-mixed
$${\rm II}.$$ The fluid is unmixed
$${\rm III}.$$ $$R{e_D} < 2300$$
$${\rm IV}.$$ $$R{e_D} > 2300$$