JEE physics Assertion & Reason

(b)

(a)

(b)

(e) Terminal velocity and critical velocity are not same. Critical velocity is the velocity below which the flow of liquid is streamline.

(c) When two holes are made in the tin, air keeps on entering through the other hole. Due to this the pressure inside the tin does not become less than atmospheric pressure which happen only one hole is made.

(a)

(d) Railways tracks are laided on large sized wooden sleepers. Due to large sized sleepers the weight of rail act on the large area. Hence, the pressure exerted is reduced appreciably.

(a) Smaller the area, larger the pressure exerted by a

(a) When a body falls through a viscous medium, finally, it attains terminal velocity. At this velocity, viscous force on rain drop balances the weight of the body.

(a)

(a) Viscosities of fluids are markedly dependent on temperature, increasing for gases and decreasing for liquids as the temperature is increased. Thus important consideration in the design of oils for engine lubrication is to reduce the temperature variation of viscosity as much as possible.

(a)

(a) According to Bernoulli's theorem, when wind velocity over the wings is larger thanthewind velocity under the wings, pressure of wind over the wings becomes less than thepressureofwind under the wing's. This provides the necessary lift to the aeroplane.

(a)

(a) The stability of a floating body depends on the relative position of centre of gravity of a body, through which its weight acts and centre of gravity of the displaced water called centre of buoyancy through which the upthrust act.

(a) Due to small area of cross-section of the hole, fluid flows out of the vessel with alarge speed and thus the fluid possesses a large linear momentum. As no external forces acts on the system, in order to conserve linear momentum, the vessel acquiresavelocityinbackwarddirection or in other words a backward thrust results on the vessel.

(c) When a body moves through a fluid, its motion is opposed by the force of fluid friction, which increases with the speed of the body. When cars and planes move through air, their motion is opposed by the air friction, which in turn, depend upon the shape of the body. It is due to this reason that the cars or planes are given such shape (known as stream lined shaped) so that air friction is minimum. Rather the movement of air layers on the upper and lower side of stream line shape provides a lift which helps in increasing the speed of the car.

(b) As a man jumps-out from a height in air with a parachute, its velocity increases first, because the gravity pull dominates the viscous drag and buoyancy of air which opposes the motion. As the velocity increases, the viscous drag of air also increases and soon a stage is reached where viscous drag and buoyancy of air balances the gravity pull. Then the man with a parachute falls with a constant velocity, called terminal velocity.

(a)

(e) Since due to applied force on liquid,thepressureistransmittedequallyinalldirectionsinside the liquid. That is why there is no fixed direction for the pressure due to liquid. Hence hydrostatic pressure is a scalar quantity.