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Final JEE - Main Exam Januar y, 2020/07-01-2020/Evening Session FINAL JEE MAIN EXAMINATION JANUARY, 2020 (Held On Tuesday 07th JANUARY, 2020) TEST PAPER WITH ANSWER PHYSICS 1. A stationary observer receives sound from two 4. identical tuning forks, one of which approaches and the other one recedes with the same speed (much less than the speed of sound). The observer hears 2 beats/sec. The oscillation frequency of each tuning fork is n0 = 1400 Hz and the velocity of sound in air is 350 m/s. The speed of each tuning fork is close to : (2) 1 m/s 2 (3) 1 m/s (4) 1 m/s 4 NTA Ans. (4) A (1) 56300 W (2) 48000 W (3) 66000 W (4) 62360 W ALLEN Ans. (3) The activity of a radioactive sample falls from 700 s 1 to 500 s 1 in 30 minutes. Its hafl life is close to : (1) 66 min (2) 52 min (3) 72 min (4) 62 min NTA Ans. (4) ALLEN Ans. (4) A aB (2) pa4 4 + 5 aA B (3) 2pa4 4 + 5 A B (4) 2pa 4 4 + 5 NTA Ans. (1) ALLEN Ans. (1) 5. The electric field of a plane electromagnetic i + j r wave is given by E = E 0 cos (kz + wt) 2 p point (x, y, z) = 0, 0, . If its instantaneous k LL An elevator in a building can carry a maximum of 10 persons, with the average mass of each person being 68 kg. The mass of the elevator itself is 920 kg and it moves with a constant speed 3 m/s. The frictional force opposing the motion is 6000 N. If the elevator is moving up with its full capacity, the power delivered by the motor to the elevator (g = 10 m/s2) must be at least : NTA Ans. (3) 3. A aB (1) 2pa4 + 4 5 At t = 0, a positively charged particle is at the ALLEN Ans. (4) 2. Mass per unit area of a circular disc of radius a depends on the distance r from its centre as s (r) = A + Br. The moment of inertia of the disc about the the axis, perpendicular to the plane and passing through its centre is : EN 1 m/s 8 (1) TIME : 2 : 30 PM to 5 : 30 PM velocity at (t = 0) is u0 k , the force acting on it due to the wave is : (1) zero (3) antiparallel to (2) parallel to i + j 2 i + j (4) parallel to k 2 NTA Ans. (3) ALLEN Ans. (3) 6. A particle of mass m and charge q has an initial r r velocity u = u0 j . If an electric field E = E 0 i and r magnetic field B = B0 i act on the particle, its speed will double after a time: 2mu0 (1) qE 0 (3) 3mu0 qE0 3mu0 (2) qE 0 (4) 2mu0 qE 0 NTA Ans. (3) ALLEN Ans. (3) 1
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