Which of the following phenomena does not involve the viscosity of air at all?
(A) Rain drops falling to ground with terminal velocity
(B) A ball spinning through air can move sideways
(C) In air flowing through a tube of variable cross section, the pressure is different at different points
(D) A meteorite burns up on entering the earth's atmosphere

A solid metallic sphere of radius r is allowed to fall freely through air. If the frictional resistance due to air is proportional to the cross-sectional area and to the square of the velocity, then the terminal velocity of the sphere is proportional to which of the following ?

Water flows through a horizontal tube of variable cross section.The area of cross section at A and B are 4 mm^2 and 2mm^2 respectively. If 1 cc of water enters per second through A find a) The speed of water at A b) the speed of river at B c) the pressure difference P_A-P_B .

a. Mark the follllowing statements as true offalse. i. A ball thrown vertically up takes moretime to go up than to come down. ii. If a ball starts fallig from the position of rest, then it travels a distance of 25 m during the third secons of tis fall. iii. A packet dropped from a rising balloon ferst moves upwards and then moves sownward as observed by a stationary observer on the ground. iv. In the absence of air resistance, all bodies fall on the surface of earth at the same rate. b. Fill in the blanks. i. When a body is thrown vertically upwards, at the highest point.........................(both belocity and accelenation are zero//only velocity is zero//ony acceleration is zero). ii. If air drag is not neglected, then which is greater: time of ascent or time of descent? iiii. A body is projected upward. Up to the maximum height time taken will be greater to travel...................... (first half//second half).

By the term velocity of rain, we mean velocity with which raindrops fall relative to the ground. In absence of wind, raindrops fall vertically and in presence of wind raindrops fall obliqucly. Moreover raindrops acquire a constant terminal velocity due air resistance very quickly as they fall toward the carth. A moving man relative to himself observes an altered velocity of raindrops. Which is known as velocity of rain relative to the man. It is given by the following equation. vec(v)_(rm)=vec(v)_(r)-vec(v)_(m) A standstill man relative to himself observes rain falling with velocity, which is equal to velocity of the raindrops relative to the ground. To protect himself a man should his umbrella against velocity of raindrops relative to himself as shown in the following figure. Rain is falling vertically with velocity 80 cm/s. (a) How should you hold your umbrella ? (b) You start walking towards the east with velocity 60 cm/s. How should you hold umbrella ? (c) You are walking towards the west with velocity 60 cm/s. How should you hold your umbrella ? (d) You are walking towards the north with velocity 60 cm/s. How should you hold your umbrella? (e) You are walking towards the south with velocity 80 cm/s. How should you hold your umbrella ?

By the term velocity of rain, we mean velocity with which raindrops fall relative to the ground. In absence of wind, raindrops fall vertically and in presence of wind raindrops fall obliqucly. Moreover raindrops acquire a constant terminal velocity due air resistance very quickly as they fall toward the carth. A moving man relative to himself observes an altered velocity of raindrops. Which is known as velocity of rain relative to the man. It is given by the following equation. vec(v)_(rm)=vec(v)_(r)-vec(v)_(m) A standstill man relative to himself observes rain falling with velocity, which is equal to velocity of the raindrops relative to the ground. To protect himself a man should his umbrella against velocity of raindrops relative to himself as shown in the following figure. When you are standstill in rain, you have to hold umbrella vertically to protect yourself. (a) When you walk with velocity 90 cm/s, you have to hold your umbrella at 53^(@) above the horizontal. What is velocity of the raindrops relative to the ground and relative to you ? (b) If you walk with speed 160 cm/s, how should you hold your umbrella ?

When a current through the medium, an electric field exists as well as a potential which varies in space. Suppose that there is a break in a high - voltage transmission line and the free end of a wire of length L is lying on the ground. An electric current flows through the regions of soil adjoining the conductor. If a man happens to be walking near by a potential difference, which is called the step voltage appears between the points where his feet touch the ground, Consequently, an electric current whose strength depends on this potential difference flows through the man. Let us calculate the step voltage. Since the conductor is quite long, we assume that the current flows from it to the ground in a direction perpendicular to the conductor. The equipotential surfaces are the surfaces of semi-cylinders whose axes coincide with the conductor. Suppose that the man is walking in a direction perpendicular to the conductor with a step of length 'b' the distance between the conductor and the foot closer to it being d. Assuming that the current flows uniformly from the conductor over the semi cylindrical region we obtain the following expression for the current density at a distance from the conductor: j=i/(pirL) In this case , the field strength along the radii perpendicular to the conductor is E_r=j/sigma=l/(pirLsigma) Consequently , the step voltage is V_(st)=int_d^(d+b) Edr =1/(pisigmaL)ln((d+b)/d) For example , If l=500A , d=1 m , b=65 cm and L=30 m we find that V_(st) =270 V. Much higher voltages may appear under other conditions and other shapes of conductors. When a part of a high- voltage transmission line falls on the ground, it creates a hazard

Hydrogen accounts for approximately 75% of the mass of the universe. Hydrogen serves as the nuclear fuel of our Sun and other stars, and these are mainly composed of hydrogen. On the earth, though hydrogen is rarely found in the uncombined state. Since the earth's gravity is too weak to hold such light molecules, nearly all the H_2 originally present in the earth's atmosphere has been lost to space. In the earth's crust and oceans, hydrogen is found in water, petroleum, proteins, carbohydrates and other compounds and it is the ninth most abundant element on a mass basis. Hydrogen has three isotopes : hydrogen or protium () , deuterium or heavy hydrogen (D or ), tritium (T or ) . The physical properties of the three isotopes are different due to the difference in their masses, i.e. isotope effect. The chemical properties of the three isotopes are similar as they have the same electronic configuration. Reaction between hydrogen and oxygen is highly exothermic, and gas mixtures that contain as little as 4% by volume hydrogen in oxygen (or in air) are highly flammable and potentially explosive. 2H_(2(g))+O_(2(g)), DeltaH^(ɵ)=-485 kJmol^(-1) As hydrogen is environmentally clean it is an enormously attractive fuel. 'Hydrogen economy' is an emerging field in which it is thought that our energy needs can be met by gaseous, liquid and solid hydrogen. As hydrogen is no a naturally occuring substance such as coal, oil or natural gas, energy must be exploaded to produce hydrogen before it can be used. Which of the following is radioactive in nature?

Hydrogen accounts for approximately 75% of the mass of the universe. Hydrogen serves as the nuclear fuel of our Sun and other stars, and these are mainly composed of hydrogen. On the earth, though hydrogen is rarely found in the uncombined state. Since the earth's gravity is too weak to hold such light molecules, nearly all the H_2 originally present in the earth's atmosphere has been lost to space. In the earth's crust and oceans, hydrogen is found in water, petroleum, proteins, carbohydrates and other compounds and it is the ninth most abundant element on a mass basis. Hydrogen has three isotopes : hydrogen or protium () , deuterium or heavy hydrogen (D or ), tritium (T or ) . The physical properties of the three isotopes are different due to the difference in their masses, i.e. isotope effect. The chemical properties of the three isotopes are similar as they have the same electronic configuration. Reaction between hydrogen and oxygen is highly exothermic, and gas mixtures that contain as little as 4% by volume hydrogen in oxygen (or in air) are highly flammable and potentially explosive. 2H_(2(g))+O_(2(g)), DeltaH^(ɵ)=-485 kJmol^(-1) As hydrogen is environmentally clean it is an enormously attractive fuel. 'Hydrogen economy' is an emerging field in which it is thought that our energy needs can be met by gaseous, liquid and solid hydrogen. As hydrogen is no a naturally occuring substance such as coal, oil or natural gas, energy must be exploaded to produce hydrogen before it can be used. Which of the following is the lightest gas?

Water flows through a horizontal tube of variable cross-section. The area of cross section at A and B are 4 mm^2 and 2mm^2 respectively. If 1 cc of water enters per seconds through. A find a. The speed of water at A, b. the speed of river at B and c. the pressure difference P_A-P_B .

Torricelli was the first do devise an experiment for measuring atmospheric pressure . He took calibrated hard glass tube , 1 m in lengt and of uniform cross section , closed at one end . He filled the whole tube with dry mercury taking care than no air or water droplets remain inside the tube , closed the opposite end of the tube tightly with thumb and inverted it . He put this inverted mercury tube into a mercury through , taking care that the end of the tube remains inside the mercury through , An interesting thing was noticed . Mercury in the tube fell down at first and then stopped at a particular position . The height was 76 cm above the free surface of mercury in the through . When the given tube was inclined or lowered in the mercury trough , the vertical haight of mercury level in the tube was always found constant . Torricelli explained this by saying that the free surface of mercury in the trough . Hence , the hydrostatic pressure exerted by the trough measures the atmospheric pressure . If an additional hole is also made at P ' at the top point of the tube , then A. mercury will not come out of the tube B. mercury may come out of the tube after some time . C. mercury will come out of the tube instantly D. none of these