#neet
- A rope is wound around a hollow cylinder of mass 3 kg and radius 40 cm. What is the angular acceleration of the cylinder if the rope is pulled with a force of 30 N ? Answer: 2. 25 rad/s ² Key idea: τ=Iα , with τ=FR and I=MR² for a hollow cylinder. τ=30×0.4=12 N m, I=3×0.4²=0.48 kg m ² . α=12/0.48=25 rad/s... 1
- Two discs of same moment of inertia rotating about their regular axis passing through centre and perpendicular to the plane of disc with angular velocities ω_1 and ω_2. They are brought into contact face to face coinciding the axis of rotation. The e… Answer: 1. 1/4 I(ω₁-ω₂)² Key idea: angular momentum is conserved when the discs join. Iω₁+Iω₂=2Iω⇒ω=ω₁+ω₂/2 . Loss =1/2Iω₁²+1/2Iω₂²-1/2(2I)ω... 1
- A gas mixture consists of 2 moles of O_2 and 4 moles of Ar at temperature T. Neglecting all vibrational modes, the total internal energy of the system is : Answer: 3. 11 RT Key idea: internal energy U=f/2nRT . O₂ is diatomic ( f=5 , vibration neglected): U=5/2×2RT=5RT . Ar is monatomic ( f=3 ):... 1
- The bulk modulus of a spherical object is 'B'. If it is subjected to uniform pressure 'p', the fractional decrease in radius is : Answer: 3. p/3B Key idea: B=p/Δ V/V , and for a sphere V∝ r³ , so Δ V/V=3Δ r/r . Δ r/r=1/3Δ V/V=p/3B . 1
- Which of the following statements are correct ?(a) Centre of mass of a body always coincides with the centre of gravity of the body.(b) Centre of mass of a body is the point at which the total gravitational torque on the body is zero.(c) A couple on… Answer: 4. (b) and (d) Key idea: check each statement. (a) False: centre of mass and centre of gravity coincide only in a uniform gravitatio... 1
- The acceleration due to gravity at a height 1 km above the earth is the same as at a depth d below the surface of earth. Then : Answer: 3. d = 2 km Key idea: at height h (small): g'=g(1-2h/R) . At depth d : g'=g(1-d/R) . Equating: 2h/R=d/R⇒ d=2h=2 km. 1
- Two blocks A and B of masses 3m and m respectively are connected by a massless and inextensible string. The whole system is suspended by a massless spring as shown in figure. The magnitudes of acceleration of A and B immediately after the string is c… Answer: 1. g/3 , g Key idea: the spring force cannot change instantly, but the string tension vanishes at once. Before cutting, the spring h... 1
- The ratio of wavelengths of the last line of Balmer series and the last line of Lyman series is : Answer: 2. 4 Key idea: the last line of a series has n₂=∞ : dfrac1λ=RZ²(dfrac1n₁²-0) . Balmer ( n₁=2 ): dfrac1λ_B=R/4 . Lyman ( n₁=1 ): dfra... 1
- A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle θ,… Answer: 4. y/2x Key idea: when a mirror rotates by θ , the reflected ray turns by 2θ . The spot moves by y=xtan2θ≈2θ x for small angles. So... 1
- A spring of force constant k is cut into lengths of ratio 1 : 2 : 3. They are connected in series and the new force constant is k'. Then they are connected in parallel and force constant is k''. Then k' : k'' is : Answer: 2. 1 : 11 Key idea: spring constant is inversely proportional to length. Pieces have lengths L/6,L/3,L/2 , so constants 6k,3k,2k . S... 1
- The diagrams below show regions of equipotentials.A positive charge is moved from A to B in each diagram. Answer: 1. In all the four cases the work done is the same. Key idea: work done by an external agent moving a charge slowly is W=q(V_B-V_A)... 1
- Suppose the charge of a proton and an electron differ slightly. One of them is -e, the other is (e+Δ e). If the net of electrostatic force and gravitational force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart… Answer: 2. 10⁻³⁷ C Key idea: each hydrogen atom then has a net charge Δ e , and the electric repulsion balances gravity. (Δ e)²/4πε₀d²=Gm_h²... 1
- A physical quantity of the dimensions of length that can be formed out of c, G and e^2/4πε_0 is [c is velocity of light, G is universal constant of gravitation and e is charge] : Answer: 4. 1/c²[Ge²/4πε₀]^(1/2) Key idea: match dimensions. e²/4πε₀ is force × length ² : [ML³T⁻²] . G=[M⁻¹L³T⁻²] . Product Ge²/4πε₀=[L⁶T⁻⁴]... 1
- Two Polaroids P_1 and P_2 are placed with their axis perpendicular to each other. Unpolarised light I_0 is incident on P_1. A third polaroid P_3 is kept in between P_1 and P_2 such that its axis makes an angle 45^° with that of P_1. The intensity of… Answer: 2. I₀/8 Key idea: the first polaroid halves unpolarised light; then use Malus's law I=Icos²θ . After P₁ : I₀/2 . After P₃ (45 ^° ):... 1
- Which of the following is made up of dead cells ? Answer: 2. Phellem Phellem (cork) is made of dead cells with suberin deposits in the walls and no protoplasm. Collenchyma, phloem (sieve ele... 1
- MALT constitutes about ______ percent of the lymphoid tissue in human body. Answer: 4. 50% Mucosa-associated lymphoid tissue (MALT) lines the respiratory, digestive and urogenital tracts. It forms about 50% of the ly... 1
- Which of the following RNAs should be most abundant in animal cell ? Answer: 4. r-RNA Among cellular RNAs, rRNA makes up about 80% of the total RNA, so it is the most abundant. tRNA is about 15%, and mRNA only... 1
- Select the mismatch : Answer: 4. textitPinus - Dioecious The mismatch is Pinus - dioecious. Pinus is monoecious: male and female cones are on the same tree. Cycas... 1
- Presence of plants arranged into well defined vertical layers depending on their height can be seen best in : Answer: 1. Tropical Rain Forest A tropical rain forest shows the best stratification, with well-defined vertical layers: emergent trees, can... 1
- Zygotic meiosis is characteristic of : Answer: 3. textitChlamydomonas In zygotic meiosis the zygote divides by meiosis first, so the plant body is haploid. This is the haplontic l... 1
- Lungs are made up of air-filled sacs, the alveoli. They do not collapse even after forceful expiration, because of : Answer: 4. Residual Volume After a forceful expiration some air still stays in the lungs. This is the residual volume, about 1100 mL to 1200... 1
- In case of poriferans, the spongocoel is lined with flagellated cells called : Answer: 2. choanocytes The spongocoel of sponges is lined by flagellated choanocytes (collar cells). Their beating drives water through the... 1
- Which one of the following is related to Ex-situ conservation of threatened animals and plants ? Answer: 4. Wildlife Safari parks Ex-situ conservation protects species outside their natural habitat, for example in zoos, botanical gardens... 1
- Which statement is wrong for Krebs' cycle ? Answer: 3. The cycle starts with condensation of acetyl group (acetyl CoA) with pyruvic acid to yield citric acid The wrong statement is opt... 1