Recent questions in JEEMAIN PAST PAPERS

Which one of the following reactions is an example of heterogeneous cataysis ?

asked Dec 11, 2018 by pady_1

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A steel meter scale is to be ruled so hat millimeter intervals are accurate within about $5 \times 10^{-5}m$ at a certain temperature. The maximum temperature variation allowable during the ruling is: (Coefficient of linear expansion of steel = $10 \times 10^{-6} K^{-1}$ )

asked Dec 11, 2018 by pady_1

1 answer

A tank with vertical walls is mounted so that its base is at a height $H$ above the horizontal ground. The tank is filled with wate to a depth $'h'$ . A hole is punched in the side wall of the tank at a depth $'x'$ below the water surface. To have maximum range of the emerging stream, the value of $x$ is :

asked Dec 11, 2018 by pady_1

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Water is conveyed through a uniform tube of 8 cm in diameter and 3140 m in length at the rate $2 \times 10^{-3} m^3$ per second. The pressure required in maintain the flow is : (Viscosity of water = $10^{-3}$ SI units )

asked Dec 11, 2018 by pady_1

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A mercury drop of radius 1 cm is sprayed into $10^6$ drop of equal size. The energy expanded in joules is : (Surface tension of mercury is $460 \times 10^{-3} N/m$ )

asked Dec 11, 2018 by pady_1

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The length of an elastic string is $'a'$ metres when the longitudinal tension is 4 N and $'b'$ meters when the longitudinal tension is 5 N. The length of the string in metres when the longitudinal tension is 9 N is :

asked Dec 11, 2018 by pady_1

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A body is executing simple harmonic motion. At a displacement $x$ its potential energy is $E_1$ and at a displacement $y$ its potential energy is $E_2$ . The potenital energy $(E)$ at displacement $(x+y)$ is :

asked Dec 11, 2018 by pady_1

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Two particles P and Q start from origin and execute simple harmonic motion along X-axis with the same amplitude but with period 3 seconds and 6 seconds respectively. The ratio of the velocities of P and Q when they meet is :

asked Dec 11, 2018 by pady_1

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Mass $M$ is divided into two parts $''xm''$ and $''(1-x)m''$ . For a given separation the value of $x$ for which the gravitational attraction between the two pieces becomes maximum is :

asked Dec 11, 2018 by pady_1

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From a uniform wire, two circular loops are made (i) $P$ of radius $'r'$ and (ii) $Q$ of radius $nr$ . If the moment of inertia of $Q$ about an axis passing through its centre and perpendicular to its plane is 8 times that of $P$ about a similar axis, the value of $'n$ is (diameter of the wire is very much smaller than $i$ or $nr$ ) :

asked Dec 11, 2018 by pady_1

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A uniform metal rod of length 'L' and mass 'M' is rotating about an axis passing through one of the ends & perpendicular to the rod with angular speed $'\omega'$ . If the temperature increases by $t^{\circ}C$ , then the change in its angular velocity is proportional to which of the following ? (Coefficient of linear expansion of rod = $\alpha$ )

asked Dec 11, 2018 by pady_1

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A particle is projected up along a rough inclined plane of inclination $45^{\circ}$ with the horizontal. If the coefficient of friction is $0.5$ , the acceleration is : (g = Acceleration due to gravity)

asked Dec 11, 2018 by pady_1

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A body of weight $''64 N''$ is pushed with just enough force to start it moving across a horizontal floor and the same force continues to act afterwards. If the coefficients of static and dynamic friction are 0.6 and 0.4 respectively, the acceleration of the body is : (acceleration due to gravity = g)

asked Dec 11, 2018 by pady_1

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The velocities of three particles of masses $20\; g, \; 30\; g$ and $50\; g$ are $10 \hat{i}, \; 10 \hat{j}$ and $10 \hat{k}$ respectively. The velocity of the centre of mass of the three particles is :

asked Dec 11, 2018 by pady_1

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A force applied by an engine on a train of mass $2.05 \times 10^6 kg$ changes its velocity from $5 \; m/s$ to $25\; m/s$ in 5 minutes. The power of the engine is :

asked Dec 11, 2018 by pady_1

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A body of mass $6 \;kg$ is under a force which causes displacement in it given by $'' s = \frac{t^2}{4}''$ metres where $'t'$ is time. The work done by the force in 2 seconds is :

asked Dec 11, 2018 by pady_1

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An object is projeced with a velocity of $20\;m/s$ making an angle of $45^{\circ}$ with horizontal. The equation for the trajectory is $"h = Ax - Bx^2"$ where $'h'$ is height, $'x'$ is horizontal distance A and B are constats. The ratio $A : B$ is : $(g = 10\;m/s^2)$

asked Dec 11, 2018 by pady_1

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A particle falls from a height 'h' upon a fixed horizontal plane and rebounds. If 'e' is the coefficient of restitution, the total distance travelled before rebound-ing has stopped is :

asked Dec 11, 2018 by pady_1

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An electron moes with speed $2 \times 10^5\; m/s$ along the positive $x$ -direction in the presence of a magnetic field of induction $\overrightarrow{B} = \hat{i} + 4 \hat{j} - 3 \hat{k}$ (in tesla). The magnitude of the force experienced by the electron in newtons is : (Charge on the electron = $1.6 \times 10^{-19}C$ )

asked Dec 11, 2018 by pady_1

0 answers

In an experiment of simple pendulum, the errors in the measurement of length of the pendulum (L) and time period (T) are 3% and 2% respectively. The maximum percentage error in the value of $\frac{L}{T^2}$ is :

asked Dec 11, 2018 by pady_1

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In CGS system magnitude of the force is 100 dynes . In another system where the fundamental physical quantities are kilogram, meter and minute, the magnitude of the force is :

asked Dec 11, 2018 by pady_1

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While a collector to emitter voltage is constant in a transistor, the collector current enhanges by $8.2\;mA$ when the emitter current changes by $8.3\;mA$ . The value of forward current ratio is :

asked Dec 11, 2018 by pady_1

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A heavy nucleus at rest breaks into two fragments which fly off with velocities in the ratio $3:1$ . The ratio of radii of the fragments is :

asked Dec 11, 2018 by pady_1

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Consider the following statements A and B and identify the correct choice in the given answers. A. Tightly bound electrons of target material scatter X-ray photon, resulting in the Compton effect. B. Photoelectric effect takes place with free electrons.

asked Dec 11, 2018 by pady_1

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The de-Broglie wavelength of an electron having $80\;eV$ energy is nearly : ( $1\;eV = 1.6 \times 10^{-19} J$ ) Mass of electron = $9 \times 10^{-31} kg$ Planck's constant = $6.6 \times 10^{-34} Js$ )

asked Dec 11, 2018 by pady_1

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Photoelectric emission is observed from a metallic surface for frequencies $v_1$ and $v_2$ of the incident light rays $(v_1 > v_2)$ . If the maximum values of kinetic energy of the photoelectrons emitted in the two cases are in the ratio of $1 : k$ , then the threshold frequency of the metallic surface is :

asked Dec 11, 2018 by pady_1

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A particle of mass $0.6 \;g$ and having charge of $25\;nC$ is moving horizontally with a uniform velocity $1.2 \times 10^4 \; ms^{-1}$ in a uniform magnetic field, then value of the magnetic induction is : $(g =10\; ms^{-2} )$

asked Dec 11, 2018 by pady_1

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If a change in current of $0.01 \;A$ in one coil produces a change in magnetic flux of $2 \times10^{-2} Wb$ in the other coil, then the mutual inductance of the two coils in henry is :

asked Dec 11, 2018 by pady_1

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A wire in the form of a square of side $'a'$ carries a current $'i'$ . Then the magnetic induction at the centre of the square is : (Magnetic permeability of free space = $\mu_0$ )

asked Dec 11, 2018 by pady_1

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Thomson coefficient of a conductor is $10\; \mu\; VK$ . The two ends of it are kept at $50^{\circ}C$ and $60^{\circ}C$ respectively. Amount of heat absorbed by the conductor when a charge of $10\; C$ flows through it, is :

asked Dec 11, 2018 by pady_1

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When a resistor of $11 \; \Omega$ is connected in series with an electric cell, the current flowing in it is $0.5 \;A$ . Instead, when a resistor of $5 \Omega$ is connected to the same electric cell in series, the current increases by $0.4 \;A$ . The internal resistance of the cell is :

asked Dec 11, 2018 by pady_1

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A closed hollow insulated cylinder is filled with gas at $0^{\circ}C$ and also contain an insulated piston of negligible weight and negligible thickness at the middle point. The gas in one side of the piston is heated to $100^{\circ}C$ . If the piston moves $5\; cm$ . The length of the hollow cylinder is :

asked Dec 11, 2018 by pady_1

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When an air bubble of radius $'r'$ rises from the bottom to the surface of a lake. Its radius becomes $\frac{5r}{4}$ (the pressure of the atmosphere is equal to the 10 m height to water column). If the temperature is contant and the surface tension is neglected the depth of the lake is :

asked Dec 11, 2018 by pady_1

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A lead bullet of mass $10\; g$ travelling at $300\; m/s$ strikes against a block of wood and comes to rest. Assuming $50 \%$ of heat is absorbed by the bullet, the increase in its temperature is : (specific heat of lead = $150 \; J/kg ^{\circ} C$ )

asked Dec 11, 2018 by pady_1

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The pressure and density of a diatomic gas $(\gamma = \frac{7}{5} )$ changes adiabatically from $(P, d)$ to $(P', d')$ . If $\frac{d'}{d} =32$ . Then $\frac{P'}{P}$ is :

asked Dec 11, 2018 by pady_1

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The wavelength of maximum intensity of radiation emitted by a star is $289.8\;nm$ . The radiation intensity of the star is : (Stefan's contant = $5.67 \times 10^{-8} \;Wm^2K^{-4}$ , constant $b = 2898\; \mu m K$ )

asked Dec 11, 2018 by pady_1

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In order to double the frequency of the fundamental note emitted by a stretched string, the length is reduced to $\frac{3}{4}^{th}$ of the original length and the tension is changed. The factor by which the tension is to be changed is :

asked Dec 11, 2018 by pady_1

1 answer

The sound waves of wavelengths 5 m and 6 m formed 30 beats in 3 seconds. The velocity of sound is :

asked Dec 11, 2018 by pady_1

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In the visible region the dispersive powers and the mean angular deviations for crown and flint glass prisms are $\omega,\; \omega'$ and $d, \; d'$ respectively. The condition of getting dispersion wih zero deviation, when the two prisms are combined is :

asked Dec 11, 2018 by pady_1

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One face of the glass prism is silver polished. A light ray falls at an angle of $45^{\circ}$ on the other face. After reflection it is subsequently reflected from the silvered face and then retraces its path. The refracting angle of prism is $30^{\circ}$ . The refractive index of the prism is :

asked Dec 11, 2018 by pady_1

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When a glass prism of refracting angle $60^{\circ}$ is immersed in a liquid its angle of minimum deviation is $30^{\circ}$ . The critical angle of glass with respect to the liquid medium is :

asked Dec 11, 2018 by pady_1

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Light waves producing interference have their amplitudes in the ratio $3:2$ . The intensity ratio of maximum and minimum of interference fringes is :

asked Dec 11, 2018 by pady_1

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The difference in the number of wavelengths, when yellow light propagates through air and vacuum columns of the same thickness, is one. The thickness of the air column is : Refractive index of air $\mu_c = 1.0003$ Wavelength of yellow light in vacuum = $6000 \; \mathring{A}$

asked Dec 11, 2018 by pady_1

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A magnet of length $10\; cm$ and magnetic moment $1\; Am^2$ is placed along side AB of an equilateral triangle ABC. If the length of the side AB is $10\; cm$ . The magnetic induction at the point 'C' is : $(\mu_0 = 4 \pi \times 10^{-7} Hm^{-1})$

asked Dec 11, 2018 by pady_1

1 answer

A magnet freely suspended in a vibration magnetometer makes $40$ oscillations per minute at place 'A' and $20$ oscillations per minute at a place 'B'. If the horizontal component of earth's maagnetic field at 'A' is $36 \times 10^{-6}T$ , then its value at 'B' is :

asked Dec 11, 2018 by pady_1

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A body of capacity $4 \; \mu F$ is charged to $80\;V$ and another body of capacity $6 \; \mu F$ is charged to $30\;V$ . When thet are connected the energy lost by $4 \; \mu F$ capacitor is :

asked Dec 11, 2018 by pady_1

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There is a uniform electric field of strength $10^3\; V\;m^{-1}$ along $y$ -axis. A body of mass $1\; g$ and charge $10^{-6}C$ is projected into the field from origin along the positive $X$ -axis with a velocity $10\; ms^{-1}$ . Its speed in $ms^{-1}$ after $10\; sec$ is : (Neglect gravitation)

asked Dec 11, 2018 by pady_1

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A $20\; F$ capacitor is charged to $5\; V$ and isolated. It is then connected in parallel with an uncharged $30\;F$ capacitor. The decrease in the energy of the system will be :

asked Dec 11, 2018 by pady_1

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Two electric charges of $9\; \mu C$ and $- 3 \; \mu C$ are placed $0.16\;m$ apart in air. There will be a point $'P'$ at which electric potential is zero on the line joining two charges and in between them. The distance of $P$ from $9 \; \mu\;C$ is :

asked Dec 11, 2018 by pady_1

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If the charge on a body is increased by 2 $C$ , the energy stored in it increases by $21 \%$ . The original charge on the body in coulomb is :

asked Dec 11, 2018 by pady_1

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