A cone with half the density of water is floating in water as shown in figure. It is depressed down by a small distance $$\delta(\ll< H)$$ and released. The frequency of simple harmonic oscillations of the cone is
Statement (A) When the temperature increases the viscosity of gases increases and the viscosity of liquids decreases.
Statement (B) Water does not wet an oily glass because cohesive force of oil is less than that of water.
Statement (C) A liquid will wet a surface of a solid, if the angle of contact is greater than $$90^{\circ}$$.
A sphere of surface area $$4 \mathrm{~m}^2$$ at temperature 400 K and having emissivity 0.5 is located in an environment of temperature 200 K. The net rate of energy exchange of the sphere is (Stefan Boltzmann constant, $$\sigma=5.67 \times 10^{-8} \mathrm{Wm}^{-2} \mathrm{~K}^4)$$
A Carnot engine operates between a source and a sink. The efficiency of the engine is $$40 \%$$ and the temperature of the sink is $$27^{\circ} \mathrm{C}$$. If the efficiency is to be increased to $$50 \%$$, then the temperature of the source must be increased by