#neet
- A car is negotiating a curved road of radius R. The road is banked at an angle θ. The coefficient of friction between the tyres of the car and the road is μ_s. The maximum safe velocity on this road is : Answer: 2. √(gRμ_s+tanθ/1-μ_stanθ) Key idea: at maximum speed friction acts down the slope, along with the normal reaction. Vertical: Ncosθ=... 1
- Consider the molecules CH_4, NH_3 and H_2O. Which of the given statements is false ? Answer: 2. The H-O-H bond angle in H₂O is larger than the H-C-H bond angle in CH₄ . Key idea: lone pairs repel more than bond pairs, so bond... 1
- In the reaction H-C CH [(2)\ CH_3CH_2Br](1)\ NaNH_2/liq.NH_3 X [(2)\ CH_3CH_2Br](1)\ NaNH_2/liq.NH_3 Y, X and Y are : Answer: 1. X = 1-Butyne ; Y = 3-Hexyne Key idea: the terminal alkyne H is acidic, so NaNH₂ removes it and the acetylide ion attacks the alky... 1
- Among the following, the correct order of acidity is : Answer: 2. HClO < HClO₂ < HClO₃ < HClO₄ Key idea: in oxoacids of the same halogen, acidity rises with the number of oxygen atoms (higher oxi... 1
- The rate of a first-order reaction is 0.04\ mol\ l^-1\ s^-1 at 10 seconds and 0.03\ mol\ l^-1\ s^-1 at 20 seconds after initiation of the reaction. The half-life period of the reaction is : Answer: 1. 24.1 s Key idea: for a first-order reaction, rate = k[A] , so the ratio of rates equals the ratio of concentrations. [A]₁₀/[A]₂₀=... 1
- Which one of the following characteristics is associated with adsorption ? Answer: 2. Δ G , Δ H and Δ S all are negative Key idea: adsorption is spontaneous, exothermic and reduces the freedom of the adsorbate. Spon... 1
- In which of the following options the order of arrangement does not agree with the variation of property indicated against it ? Answer: 3. I < Br < Cl < F (increasing electron gain enthalpy) Key idea: compare each series with the real trend. Option 1: isoelectronic io... 1
- Which of the following statements is false ? Answer: 3. Ca²⁺ ions are not important in maintaining the regular beating of the heart. Key idea: mathrmCa²⁺ and mathrmMg²⁺ both have import... 1
- Which of the following statements about hydrogen is incorrect ? Answer: 1. Hydrogen has three isotopes of which tritium is the most common. Key idea: check each statement against NCERT facts and pick the... 1
- The correct statement regarding a carbonyl compound with a hydrogen atom on its alpha-carbon, is : Answer: 4. a carbonyl compound with a hydrogen atom on its alpha-carbon rapidly equilibrates with its corresponding enol and this process is... 1
- MY and NY_3, two nearly insoluble salts, have the same K_sp values of 6.2×10^-13 at room temperature. Which statement would be true in regard to MY and NY_3 ? Answer: 2. The molar solubility of MY in water is less than that of NY₃ . Key idea: compare solubilities from the K_sp expression for each s... 1
- In a protein molecule various amino acids are linked together by : Answer: 3. peptide bond Key idea: amino acids join through the amide linkage between the -COOH of one and the -NH₂ of the next, formed by lo... 1
- From a disc of radius R and mass M, a circular hole of diameter R, whose rim passes through the centre is cut. What is the moment of inertia of the remaining part of the disc about a perpendicular axis, passing through the centre ? Answer: 2. 13 MR²/32 Key idea: remaining part = full disc minus the cut-out disc, using the parallel axis theorem for the hole. Full disc: I... 1
- A square loop ABCD carrying a current i, is placed near and coplanar with a long straight conductor XY carrying a current I, the net force on the loop will be : Answer: 1. 2μ₀ Ii/3π Key idea: forces on the two sides parallel to the wire add up; forces on the other two sides cancel. Side nearest the w... 1
- The magnetic susceptibility is negative for : Answer: 1. diamagnetic material only Key idea: only diamagnetic materials get magnetised opposite to the applied field. Diamagnetic: chi sma... 1
- A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15\ ms^-1. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is : (Take velocity of sound in air = 330\ ms^… Answer: 3. 838 Hz Key idea: the cliff is a stationary reflector. The sound reaches it with a Doppler shift because the siren moves toward th... 1
- A capacitor of 2\ μ F is charged as shown in the diagram. When the switch S is turned to position 2, the percentage of its stored energy dissipated is : Answer: 4. 80% Key idea: charge is conserved; it is shared between the capacitors until the potentials are equal, and the difference in ener... 1
- In a diffraction pattern due to a single slit of width 'a', the first minimum is observed at an angle 30^° when light of wavelength 5000 Å is incident on the slit. The first secondary maximum is observed at an angle of : Answer: 4. sin⁻¹(3/4) Key idea: single-slit minima satisfy asinθ=nλ ; secondary maxima are approximately at asinθ=(n+1/2)λ . First minimum a... 1
- At what height from the surface of earth the gravitation potential and the value of g are -5.4×10^7\ J kg^-2 and 6.0\ ms^-2 respectively ? Take the radius of earth as 6400 km : Answer: 1. 2600 km Key idea: V=-GM/r and g=GM/r² , so r=|V|/g . r=dfrac5.4×10⁷6.0=9.0×10⁶ m =9000 km. Height h=r-R_E=9000-6400=2600 km. 1
- Out of the following options which one can be used to produce a propagating electromagnetic wave ? Answer: 4. An accelerating charge Key idea: electromagnetic waves are produced by accelerated (time-varying) charges. A charge at constant v... 1
- Two identical charged spheres suspended from a common point by two massless strings of lengths l, are initially at a distance d (d << l) apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a… Answer: 3. v ∝ x^(-1/2) Key idea: at equilibrium, the electric force balances the horizontal component of tension. With tanθ≈x/2l : kq²/x²=m... 1
- A uniform rope of length L and mass m_1 hangs vertically from a rigid support. A block of mass m_2 is attached to the free end of the rope. A transverse pulse of wavelength λ_1 is produced at the lower end of the rope. The wavelength of the pulse whe… Answer: 2. √(m₁+m₂/m₂) Key idea: the frequency of a pulse stays the same, so wavelength is proportional to wave speed v=√(T/μ) . At the lowe... 1
- A refrigerator works between 4^° C and 30^° C. It is required to remove 600 calories of heat every second in order to keep the temperature of the refrigerated space constant. The power required is : (Take 1 cal = 4.2 Joules) Answer: 3. 236.5 W Key idea: for a refrigerator, COP=T₂/T₁-T₂=Q₂/W . T₂=277 K, T₁=303 K, so COP =277/26≈10.65 . Heat removed per second =600... 1
- An air column, closed at one end and open at the other, resonates with a tuning fork when the smallest length of the column is 50 cm. The next larger length of the column resonating with the same tuning fork is : Answer: 3. 150 cm Key idea: a closed pipe resonates at odd multiples of λ/4 : lengths L, 3L, 5L,dots Smallest length =λ/4=50 cm. The next re... 1