Doubtly
@Doubtly · Joined Feb 2021
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- In Δ ABC (a – b)2 cos2 2 c + (a + b)2 sin2 2 c = Correct answer is C² https://youtu.be/l-lf4ykAdtk Instead of pythagoras You can use this formulas cos(C) = a² + b² − c²over 2ab 1
- If r.v. X : waiting time in minutes for bus and p.d.f. of X is given by The correct answer is option b) 0.8 f(x)= \1/5,/0, \ \ 0≤ x≤ 5, /otherwise, Solution will come soon 1
- Three identical masses m are kept at the vertices of equilateral Δ of side ‘a’. Answer is sqrt3 Gm²/a² 1
- The sum of two numbers is 128 and their difference is 16. Find the numbers. Let the two numbers be x and y According to 1^st condition , x+y=128 ------1 According to 2nd condition , x-y=16 --------2 Adding equation 1... 1
- 5 Chairs and 4 Tables Together Cost ₹5600, While 4 Chairs and 3 Tables Together Cost ₹ 4340. Find the Cost of Each Chair and that of Each Table Video solution:: https://youtu.be/mG1XSNDtBig Text Solution Let the cost of a chair be ₹ x and that of a table be ₹ y, then 5x + 4y = 5600 …... 1
- 5 books and 7 pens together cost Rs 79 whereas 7 books and 5 pens together cost Rs 77, find the total cost of 1 book and 2 pens. Let the cost of a book be Rs x and that of a pen be Rs y. Then, 5x + 7y = 79 .....(i) 7x + 5y = 77 ....(iii) Multiplying equation (i) by 5 a... 1
- Shabana’s age 10 year hence will be twice as Juhi’s present age. The correct answer is shabanas age is 26 years and juhis age is 18 years Video solution::: https://youtu.be/g0836O7_m4A 1
- Uncertainty in position of a particle of 25 g in space is 10–5 m. Hence, uncertainty in velocity (m s–1) is (Planck’s constant, h = 6.6 × 10–34 Js) Correct option is (a) 2.1 × 10^(–28) Explaination:: mass=25g=25 × 10⁻³ kg , Δx=10⁻⁵m According to Heisenberg uncertainty principle triangle... 1
- In a hydrogen atom, if the energy of an electron in the ground state is – 13.6 eV, then that in the 2nd excited state is Answer: −1.51 eV For hydrogen the energy of the n th orbit is E_n = -frac13.6n²\ eV The ground state is n = 1 , the first excited state is n... 1
- Which of the following ions has the maximum magnetic moment ? Correct option is (a) Mn²⁺ Explaination ::: number of unpaired electrons in Mn²⁺ =5 number of unpaired electrons in Fe²⁺ =4 number of unpair... 1
- Energy of H-atom in the ground state is –13.6 eV, hence energy in the second excited state is Correct answer is option (c) –1.51 eV Explaination:: 2 ^nd\ excited \ state \ n=3 E n =− 13.06/n² -By formula E₃=-13.06/3²=-13.06/9 = -1.51... 1
- a.When the gas formed on heating limestone is passed through freshly prepared lime water, the lime water turns milky i. When limestone (CaCO₃) is heated; it undergoes decomposition reaction giving calcium oxide (CaO) and carbon dioxide (CO₂) as products. ii... 1
- d. Displacement reaction 3. Explain the following terms with examples. The reaction in which the place of the ion of a less reactive element in a compound is taken by another more reactive element by formation o... 1
- c. Balanced equation 3. Explain the following terms with examples. A chemical equation in which the number of atoms of the elements in the reactant is same as the number of atoms of the elements in the produ... 1
- b. Combination reaction 3. Explain the following terms with examples. When two or more reactants combine in a reaction to form a single product, it is called a combination reaction. Example:: When HCl vapours s... 1
- There is a stream of neutrons with the kinetic energy of 0.0327 eV. The kinetic energy of neutron is displaystyle 1/2mu²=0.0327× 1.6× 10⁻¹⁹J --the unit eV is converted to J by multiplying with 1.6×10⁻¹⁹ The m... 1
- There is a stream of neutrons with a kinetic energy of 0.0327 eV. The kinetic energy of neutron is displaystyle 1/2mu²=0.0327× 1.6× 10⁻¹⁹J --the unit eV is converted to J by multiplying with 1.6×10⁻¹⁹ The m... 1
- A big dumb-bell is prepared by using a uniform rod of mass 60 g and length 20 cm. Two identical solid spheres of mass 50 g Answer: I = 46000\ mathrmg cm² = 4.6×10⁻³\ mathrmkg m² Given: rod M_r = 60\ g , L = 20\ cm ; each sphere M_s = 50\ g , R_s = 10\ cm . Distan... 1