A flexible rotor-shaft system comprises of a $$10kg$$ rotor disc placed in the middle of a mass-less shaft of diameter $$30$$ $$mm$$ and length $$500mm$$ between bearings (shaft is being taken mass-less as the equivalent mass of the shaft is included in the rotor mass) mounted at the ends. The bearings are assumed to simulate simply supported boundary conditions. The shaft is made of steel for which the value of $$E$$ is $$\,2.1\, \times \,{10^{11}}\,$$. Pa. What is the critical speed of rotation of the shaft?

A uniform rigid slender bar of mass $$10$$ $$kg.$$ is hinged at the left end is suspended with the help of spring and damper arrangement as shown in the figure where $$K = 2kN/m,$$ $$C =500Ns/m$$ and the stiffness of the torsional spring $${K_\theta }$$ is 1 kN/m/rad. Ignore the hinge dimensions.

The un-damped natural frequency of oscillations of the bar about the hinge point is

A uniform rigid slender bar of mass $$10$$ $$kg.$$ is hinged at the left end is suspended with the help of spring and damper arrangement as shown in the figure where $$K = 2kN/m,$$ $$C =500Ns/m$$ and the stiffness of the torsional spring $${K_\theta }$$ is 1 kN/m/rad. Ignore the hinge dimensions.

The damping coefficient in the vibration equation is given by

Nitrogen gas (molecular weight $$28$$) is enclosed in a cylinder by a piston, at the initial condition of $$2$$ bar, $$298$$ $$K$$ and $$1\,\,{m^3}$$. In a particular process, the gas slowly expands under isothermal condition, until the volume becomes $$2{m^3}.$$ Heat exchange occurs with the atmosphere at $$298$$ $$K$$ during this process.

The entropy change for the system during the process in $$kJ/K$$ is