Question 1:
easyAssertion (A): A raindrop after falling through some height attains a constant velocity.
Reason (R): At constant velocity the viscous drag plus buoyant force is just equal to its weight.
Assertion (A) is true, as falling objects in a fluid reach terminal velocity when resistive forces balance gravity.
Reason (R) is true, stating the force balance condition for constant velocity: Weight = viscous drag + buoyant force. (R) correctly explains (A).
Question 2:
easyAssertion (A): Water flows faster than honey.
Reason (R): The co-efficient of viscosity of water is less than honey.
Concept: Viscosity and fluid resistance. Viscosity is a measure of a fluid's resistance to flow. A fluid with lower viscosity flows more easily and thus faster. Water has a significantly lower coefficient of viscosity than honey. Both Assertion and Reason are true, and Reason correctly explains Assertion.
Question 3:
easyAssertion (A): The angle of contact of a liquid decreases with increase in temperature.
Reason (R): With increase in temperature, the surface tension of liquid increases.
Concept: Effect of temperature on liquid properties. Assertion (A) is true; generally, the angle of contact decreases with increasing temperature as intermolecular forces weaken. Reason (R) is false; surface tension of a liquid *decreases* with an increase in temperature, not increases, because the kinetic energy of molecules increases, reducing cohesive forces.
Question 4:
easyAssertion (A): The shape of a liquid drop is spherical.
Reason (R): The pressure inside the drop is greater than that of outside.
Concept: Surface tension and pressure difference. Assertion (A) is true because surface tension tends to minimize the surface area of a liquid for a given volume, and a sphere has the minimum surface area. Reason (R) is true; due to surface tension, there is an excess pressure inside a spherical liquid drop, given by \(P_{in} - P_{out} = \frac{2T}{R}\). This excess pressure balances the inward pull of surface tension, thus R correctly explains A.
Question 5:
easyAssertion (A): Surface energy of an oil drop is same whether placed on glass or water surface.
Reason (R): Surface energy is dependent only on the properties of oil.
Concept: Interfacial surface energy. Surface energy (or surface tension) is a property of the interface between two phases. It depends on the intermolecular forces between the molecules of *both* substances forming the interface. Therefore, an oil-glass interface will have different surface energy than an oil-water interface. Both Assertion and Reason are false.