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Showing posts from October, 2020

A nucleus is at rest in the laboratory frame of reference. Show that if it disintegrates into two smaller nuclei the products must move in opposite directions.

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Ques : A nucleus is at rest in the laboratory frame of reference. Show that if it disintegrates into two smaller nuclei the products must move in opposite directions. Ans : Let m, m1, and m2 be the respective masses of the parent nucleus and the two daughter nuclei. The parent nucleus is at rest.   Initial momentum of the system (parent nucleus) = 0 Let v 1 and v2 be the respective velocities of the daughter nuclei having masses m1 and m2. Total linear momentum of the system after disintegration = m1 v 1 + m2 v2 According to the law of conservation of momentum: Total initial momentum = Total final momentum 0 = m1 v 1 + m2 v2 v 1 = - m2 v2 / m1 Here, the negative sign indicates that the fragments of the parent nucleus move in directions opposite to each other.
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A rocket with a lift-off mass 20,000 kg is blasted upwards with an initial acceleration of 5.0 m/s². Calculate the initial thrust (force) of the blast.

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Ques : A rocket with a lift-off mass 20,000 kg is blasted upwards with an initial acceleration of 5.0 m/s². Calculate the initial thrust (force) of the blast. Ans : Mass of the rocket, m = 20,000 kg Initial acceleration, a = 5 m/s2 Acceleration due to gravity, g = 10 m/s2 Using Newton’s second law of motion, the net force (thrust) acting on the rocket is given by the relation: F – mg = ma F = m (g + a) = 20000 × (10 + 5)  = 20000 × 15  = 3 × 10^5 N. 
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Find the sum of all odd integers from 1 to 1001.

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Ques : Find the sum of all odd integers from 1 to 1001.  Ans : The odd integers from 1 to 1001 are 1,3,5,7, ..., 999, 1001. This is an AP in which a=1, d=(3-1)×2 and I = 1001.  Let the number of terms be n. Then, an = 1001 an = a + (n-1) d = 1001  1 + (n- 1) x 2 = 1001  n= 501.  Thus, a=1, l= 1001 and n = 501. Sn = n(a+l) / 2 = 501(1 + 1001) / 2  = 251001.  Hence, the required sum is 251001.
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Chemical Bonding and molecular structure Multiple choice questions (MCQs) || Chemical bonding MCQs || Chapter 4 class 11 Chemistry MCQs || Part 3rd ||

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Ques 21: Which of the following molecules does not contain a lone pair of electrons ? (a)  N H 3 (b)  P F 5 (c)  H 2 O   (d)  S F  4 Ans : (b)  P F 5 Ques 22: Hydrogen bond is strongest in (a) S-H.....O  (b) 0-H.....S (c) F- H.....F  (d) F- H...O  Ans : (c) F- H.....F Ques 23: The pair likely to form strongest hydrogen bonding is (a)  H2 O2  and  H 2 O (b) H C OOH and C H  3 COOH (c) C  H  3 COOH and C  H  3 COOC  H  3 , (d)  Si H  4  and  Si Cl  4 Ans : (b) H C OOH and C  H  3 COOH Ques 24: Which of the following has highest boiling point? (a)  N H 3 (b)  P H 3 (c)  Sb H 3 , (d) As H 3 Ans : (a)  N H 3 Ques 25: The calculated bond order in O, ions is :  (a) 1 (b) √1 (c) 2 (d) √2 Ans : (b) √1 Ques 26: In which of the following molecules, the central atom has two lone pairs of electrons ? (a)  S F...
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Formula for kinetic energy || kinetic energy formula || Derivation of kinetic energy ||

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 Kinetic Energy of a body can be obtained either from (i) the amount of work done in stopping the moving body, or from (ii) the amount of work done in giving the present velocity to the body from the state of rest.  Let us use the second method: Suppose, m = mass of a body at rest (i.e., u=0).                   F = Force applied on the body                   a = acceleration produced in the body                            in the direction of force applied.                   v = velocity acquired by the body in                               moving through a distances.  From,                  v²- u² = 2 a s         ...
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Motion in a straight line Important questions of physics || Linear motion important question || Short Questions || PHYSICS || KINEMATICS 1 D ||

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Ques 1 : What is meant by a point object in physics? Ans : An object is said to be a point object if it is dimensionless [MⁿLⁿTⁿ , n= 0]. And the path in which it travels is much larger in compare to the mass of the object.  Ques 2: Is it true that a body is always at rest in a frame which is fixed to the body itself? Ans : Yes, because relative velocity with respect to frame of reference is zero. Ques 3 : Discuss if a body moving with uniform velocity is in equilibrium. Ans :  Net force on the body is zero. Net acceleration of the body is zero and the force is product of mass and acceleration. Hence, the net force on the body is zero.  Ques 4 : What does the speedometer records−the average speed or the instantaneous speed?  Ans : It records (or measures) the instantaneous speed(Speed at a particular interval of time) at an instant of time.   Ques 5 : Which motion is exactly represented by ∆𝒔 = 𝒖∆𝒕. Ans : It represents the motion with uniform velocit...
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Chemical Bonding and molecular structure Multiple choice questions (MCQs) || Chemical bonding MCQs || Chapter 4 class 11 Chemistry MCQs || Part II ||

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11. Which of the following would have a permanent dipole moment?  (a) Si F  4 (b) S  F  4 (c) X e  F  4 (d)  B F 3 Ans :  (b) S  F  4 12. Which of the following molecule/ion does not contain unpaired electrons ? (a) N molecule (b)   O 2    +  2 electron (c) O 2 (d) B molecule Ans :  (b)   O 2    +  2 electron 13. The percentage ionic character of a bond having 1.275 Å its length and 1.03 D its dipole moment is: (a) 10% (b) 15% (c) 16.83%  (d) 18.8%. Ans : (c) 16.83%  14 . The angle between covalent bonds is maximum in (a)  C H  4 (b)  B F  3 (c)  P F  3 (d)  N H  3 Ans : (b)  B F  3 15. The percentage character of the hybrid orbitals in methane, ethene and ethyne are (a) 25, 50, 75  (b) 25, 33,75 (c) 25, 33, 50 (d) 100, 50, 25 Ans : (c) 25, 33, 50 16. Carbon dioxide is iso structural with (a) Tin chloride (b) Zinc chl...
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Chemical Kinetics || Class 12 Chapter 4 || Chemistry Part 1 ||

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                   1. Introduction Chemistry is full of changes. During any chemical reaction we have to notice these changes. For any chemical reaction, chemists try to find out: (a) the feasibility of a chemical reaction which can be predicted by thermodynamics ( as we know that the reaction with ∆G < 0, at constant temperature and the pressure is feasible); (b) the extent to which a reaction will be proceed can be determined from the chemical equilibrium; (c) speed of a reaction i.e. time taken by a reaction to reach equilibrium. Along with feasibility and extent, it is equally important to know the rate and the factors controlling the rate of a chemical reaction for its complete understanding. The word kinetics is derived from the Greek word ‘kinesis’ meaning movement. Thermodynamics tells only about the feasibility of a reaction whereas chemical kinetics tells about the rate of a chemical reaction. For example, thermodyna...
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Di nitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation

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Ques : Di nitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation:                        N 2 ​ +  H 2  ​ (g)→2  NH 3  ​   (i) Calculate the mass of ammonia produced if 2.00×10 2 g di nitrogen react with 1.00×10 3 g of dihydrogen.  (ii) Will any of the two reactants remain un reacted? (iii) If yes, which one and what would be its mass? Ans : (i) 28.0 g of  N 2  require 6.0 g of  H 2  to produce =34.0 g of NH  ​    2.00 × 10³ g of N 2  will produce = 28/34 ×2.00×10³g of  NH 3    =2.43×10³ g of  NH 3                  = 2430 g  NH 3 ​   (ii) Yes, dihydrogen will remain un reacted to some extent.  (iii) Amount of hydrogen that remains un reacted. 28.0 g of N 2  require 6.0 g of  H 2 ​   2.00 g×1...
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Chemical Bonding and molecular structure Multiple choice questions (MCQs) || Chemical bonding MCQs || Chapter 4 class 11 Chemistry MCQs ||

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1. In which of the following, the bond angle between two covalent bonds is the maximum ? (a) H 2 O (b) NH 3 (c)  CO 2 (d) CH 4 Ans : (c) CO 2 2. The hybridisation of C involved in acetylene is  (a) s p² (b) s p³ (c) s p (d) d s p² Ans: (c) s p 3. Which of the following is not correct resonating structure for carbon dioxide ? (a) O=C=0  (b) O - C=0  (c) 0 - C =0  (d) O= C - O Ans: (c) 0 - C =0 4. Which of the following has maximum covalent character? (a) Li I (b) Li F (c)  Li Cl (d) Li Br. Ans: (a) Li I 5. Which of the following exception to octet rule? (a) BF 3 (b)  PF 5 (c)  CO 2 (d) I F 7 Ans: (c)  CO 2 6. For which of the following hybridisation the bond angle is maximum ? (a) s p² (b) s p³ (c) s p (d) d s p² Ans: (c) s p 7. Which one has minimum dipole moment ? (a) Butene-1 (b) cis-Butene-2 (c) trans-Butene-2 (d) 2-Methyl propene. Ans: (c) trans-Butene-2 8. Which of the following has highest lattice energy?  (a) L...
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LAWS OF CHEMICAL COMBINATION

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      LAWS OF CHEMICAL COMBINATION In this topic we will learn about the various laws that are involved during the formation of chemical reaction. The observation during the chemical changes, are made of certain generalisation These generalisations are known as laws of chemical combination. These are: 1. Law of conservation of mass  2. Law of constant composition or definite proportions 3. Law of multiple proportions 4. Law of reciprocal proportions 5. Law of combining volumes 1. Law of Conservation of Mass This law deals with the relation between the mass  of the reactants and the products during the chemical changes. It was postulated by a French the Antoine Lavoisier (Father of chemistry) in 1789. He performed chemical experimental studies for combustion reactions before concluding the law.  Law of conservation of mass states that “  during any physical or chemical change, total mass of the products is equal to total mass of the reactants”. In other...
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Important Multiple Choice Questions of physics || Class 11 ||

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1. A particle moves along a straight-line y= 3x + 5. Which coordinate changes at faster rate? a) X- coordinate  b) y-coordinate  c) both x and y  d) insufficient data Ans: b) y-coordinate ( Let suppose x=1,then y=8 ,x= 2 ,y = 11. So y coordinate is increasing 3 times faster as compare to X- coordinate  ) .  2. If 𝐴⃗ + 𝐵⃗⃗ = 𝐶⃗ and A+B = C then the angle between 𝐴⃗ and 𝐵⃗⃗ is- a) 0 b) π/4  c) π/2  d) π  Ans: c) π/2 3. If a unit vector is represented by 0.5𝑖− 0.8𝑗+ c k then the value of ‘c’ is- a) 1  b) √0.11  c) √0.01 d) √0.39 Ans: b) √0.11 4. Given that A = B. what is the angle between (𝐴⃗ + 𝐵⃗⃗) and (𝐴⃗ − 𝐵⃗⃗⃗⃗⃗⃗⃗⃗) =? a) 30° b) 60° c) 90° d) 180° Ans: d) 180° 5. What is the component of the (3i+4j) along (i + j)? a) ½ (i + j)  b) 3/2(i + j)  c) 5/2 (i + j)  d) 7/2 (i + j) Ans: d) 7/2 (i + j) 6. What is the value of (𝐴⃗ + 𝐵⃗⃗).( 𝐴⃗ × 𝐵⃗⃗)? a) 0  b) A²-B² c) A²+B²+2AB  d) None of these Ans...
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QUANTUM NUMBERS (Principal, Azimuthal, Magnetic and Spin)

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                  QUANTUM NUMBERS  Orbitals represent regions in the space around the nucleus where the probability of finding the electron is maximum. A large number of electron orbitals are possible in atom. These can be distinguished by their size, shape and orientation of the orbitals. To describe each electron in an atom in different orbitals, we need a set of three numbers known as quantum numbers. These are designated as n, l and m. In addition to these three numbers another quantum number is also needed which specifies the spin of the electron. These four numbers are called quantum numbers. These are discussed below: 1. Principal quantum number (n) :  This quantum number determines the main energy shell or level in which the electron is present. It is denoted by n. It can have whole number values starting from 1 such as n = 1, 2, 3, 4 ... This quantum number also identifies as shell. The shell with n 1 is called the first sh...
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Diagonal Relationship between Beryllium and Aluminium || Relation between Beryllium and Aluminium

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  Diagonal Relationship between Beryllium and Aluminium The ionic radius of Beryllium (Be 2+) is estimated to be nearly 31 pm; the charge/radius ratio Or e/m ratio is nearly the same as that of the Al 3+ ion. Hence beryllium resembles aluminium in these ways. Some of the similarities are given below: » Like Aluminium, Beryllium(be) is not readily attacked by acids H+ donor because of the formation of an oxide film on the surface of the metal by reacting with oxygen, i.e. they are rendered passive by nitric acid. » Beryllium hydroxide[[Be(OH)4]2] dissolves in excess of alkali to give a beryllate ion, [ Be(OH)4]2– just as aluminium hydroxide[Al(OH)3] gives aluminate ion, [Al(OH)4] » The chlorides of metals beryllium and aluminium have Cl– bridged chloride structure in vapour phase. Both the chlorides are soluble in organic solvents and are strong as Lewis acids They are used as Friedel Craft catalysts. » Beryllium(Be) and aluminium(Al) ions have strong tendency to form complexes, (Be...
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Math question

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A tower, x metre, has a flagstaff at its top. The tower and flagstaff subtends equal angles at a point distant y metre from the foot of the tower. Then find the length of the flagstaff ( in metre). 
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Solar System, Planets, Moons, Asteroid Belt,Kuiper Belt and Oort Cloud, Comets and Meteoroids

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 The solar system consists of the Sun, which is a star at its center, and all the celestial bodies bound by its gravitational pull. These bodies include planets, moons, asteroids, comets, and other objects. Key Components of the Solar System: The Sun : The Sun is the center of the solar system and contains about 99.86% of its mass. It is a star primarily composed of hydrogen and helium, providing the heat and light that sustains life on Earth. Planets : There are eight recognized planets in the solar system: Mercury : The closest planet to the Sun, known for extreme temperature variations and no atmosphere. Venus : Similar in size to Earth but with a thick, toxic atmosphere and surface temperatures hot enough to melt lead. Earth : The third planet from the Sun, the only known planet to support life, with water and a breathable atmosphere. Mars : Known as the Red Planet, it has a cold, dry surface and signs of past water. Jupiter : The largest planet, a gas giant, w...
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