COMPUTER BASED TEST (CBT) Concept Based Questions & Solutions

Transcription

1 PAPER- (B.E./B. TECH.) JEE (Min) 9 COMPUTER BASED TEST (CBT) Concept Bsed Questions & Solutions Dte: 9, 9 (SHIT-) TIME : (9.3.m. to.3 p.m) Durtion: 3 Hours Mx. Mrks: 36 SUBJECT :PHYSICS

2 JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS PART : PHYSICS Striht Objective Type This section contins 3 multiple choice questions. Ech question hs choices (), (), (3) nd () for its nswer, out of which Only One is correct.. A block of mss k is kept on rouh inclined s shown in fiure. The coefficient of friction between the block nd the surfce is.6. Two forces of mnitude 3N & P Newton re ctin of the block s shown fiure. If friction on the block is ctin upwrds then minimum vlue of P for which the block remins t rest is : P k 3N µ.6 5 () 6 N () 3 N (3) N () 3 N Ans. () m sin θ + 3 P + friction m sin θ + 3 P + µm cos θ. + 3 P P 3.8 P P 3N. P B C A D V or pth ABC, Het iven to the system is 6 J nd work done by the system is 3 J. or pth ADC, work done by the system is J. The het iven to the system for pth ADC is () J () 8 J (3) J () 6 J Ans. (3) or ABC Q U + W 6 U + 3 ; U 3 J or ADC Q U + W 3 + J PAGE #

3 3. JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS O Initilly n object is kept t distnce of cm from the convex lens nd shrp ime is formed t cm hed of lens on the screen. Now lss plte of µ.5 cm nd thickness.5 cm is plced between object nd lens. The distnce by which the screen be shifted to et shrp ime on the screen will be () 9 5 cm () 5 9 cm (3) cm () 5 cm Ans. () Screen cm cm f cm so f 5 cm Now due to lss plte shift t.5.5cm µ 3 So new u cm v f u v v Ans V So, shift A plnet of mss m hvin nulr momentum L is revolvin round the sun. The eril velocity of the plnet will be r dθ r Ans. () () L m () L m (3) L m () L m d r dθ da d θ dt r dt da dt r ω L mr ω L m PAGE #

4 JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS 5. The velocity of prticle v t ny instnt is v y î + x ĵ. The eqution of trjectory of the prticle is : () x + y constnt () y x + constnt (3) xy constnt () None of these Ans. () dx dt y dy dt x dx dy y x y x + c 6. Initilly block of mss M is t rest on frictionless floor nd the sprin is in relxed condition A constnt force is pplied on the block s shown in fiure. The mximum velocity of block is : () () (3) () mk mk mk mk Ans. () K m When Vmx. cc n x K Apply W.E.T. Wsp W K.E. Kx +.x K.E. K K K mu mx. K mk Vmx. mu mx. 7. Mnetic field t point O is A cm 5 3 cm ().5 5 () 5 (3) 5 () O PAGE # 3

5 JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS Ans. () µ Mnetic field t centre of n re subtendin nle Q t the centre π r µ π B π 3 5 π π B 3 π Chre Q is uniformly distributed over rin of rdius R. The heiht h, on the xis of the rin t which electric field is mximum P h R () R () R (3) R () None of these Ans. () Electric field t distnce x on the xis of rin from the centre is kqx 3/ E (R + x ) 3/ 3 / (R x ) x. (R x ) x de + + K 3 dx (R + x ) R + x 3x R x x ± R 9. Two rdioctive elements A & B hve initil ctivity curie & curie respectively. If A hs twice the no. of moles s tht of B. The decy constnt λa & λb cn be () (, 5) () (5, ) (3) (, ) () (5, ) Ans. () Activity λ N λana λbnb λa NA λ N B B λa λb λ A λ B PAGE #

6 JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS. A conducin loop of resistnce Ω nd re m is plced in uniform nd time vryin mnetic field B. sin (5πt). The Chre pssin throuh the loop in t to t ms is : () µc () 7 µc (3) 8 µc () µc Ans. () t ms φ Q, φ BAdt R φ Q t ms 3. sin(5π t) 3.5 dt µc. If current in current crryin wire is.5a, number of free electrons per unit volume is 8 8 m 3 nd re of cross section is 5 mm. Drift velocity of electrons will be (). mm/s () mm/s (3). mm/s () None of these Ans. () i neavd vd.5 3 vd vd. mm/s 6. L T A B L/ L/ L/ T L If temperture difference T T is C. The temperture difference between points A & B is () 3 () 5 (3) 6 () 75 Ans. () R/ A R B R/ T R/ R/ R T T TA TB T 3R 3 8R PAGE # 5

7 3. JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS m v m e e M Three blocks m, m nd M re kept on frictionless floor s shown in fiure. The left most block is iven velocity v towrds riht. All the collisions between the blocks re perfectly inelstic. The loss in kinetic enery fter ll the collisions is 5/6 th of initil kinetic enery. The rtio of M/m will be : () /8 () / (3) () Ans. (3) mv (m + M)v' mv v' m + M Initil enery inl enery mv mv mv (m + M) m + M mv m + M mv mv m + M 6 m M M m m + M 6 m ( V ) RMS He. In mixture mole of He nd mole of Ar is present. ind ( V RMS ) Ar t 3 k. () 6.3 ().58 (3) 3.6 () Ans. (3) ( VRMS) He M Ar V MHe 3.6 ( RMS ) Ar 5. Liht of wvelenths λ 3 nm nd λ 5 nm re incident on metllic surfce. If the rtio of the speed of the electrons ejected is. The work function of the metl is () ev ().85 ev (3).5 ev () ev Ans. () PAGE # 6

8 hc φ+ m(v) λ hc φ+ m(v) λ hc hc 3 mv λ λ JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS hc hc mv 3 λ λ hc mv λ φ hc hc hc hc hc + λ 3λ 3λ 3 λ 3λ ev ev.85 ev Vlue of i (Ampere) when switch is closed is. i 3 V Ω Ω i V Ω i () () 5 (3) () Ans. () v V Ω Ω Ω i3 + i i v v + v V v i 5 Amp. PAGE # 7

9 JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS 7. If net force on chre kept t O is zero. The vlue of chre q is : d/ d () Ans. () Q + () KQq KQ + d / d q + Q q Q +Q q +Q (O) Q (3) Q + () Q 8. If vlue of electric field E volt/m for electromnetic wve. The vlue of mnetic field B will be : () 5 9 T (). 9 T (3) 5 T (). T Ans. () E B C 7 E 6.3 B 9. C Given, d>>> If force ctin on loop is then : i d i () () (3) d Ans. (3) () d d PAGE # 8

10 JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS θ +m θ d x x orce on one pole µ m π d + x Totl force sinθ. µ m π d + π µ mx ( d + ) m d x + m x M π (mnetic moment) Totl force µ ( + ) d µ d (As d >>). Two coherent liht sources hvin intensity nd. If rtio of Ans. () 6 () () 6 9 (3) mx min is 6 :. ind () 5 9? If lenth of resistnce wire is incresed by.5 % keepin the volume constnt then chne in resistnce will be : () % () % (3).5% () % Ans. () PAGE # 9

11 .5% A.5% A R ρ A R A R A R R JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS.5% +.5% %. A uniform L shped rod ech of side A is held s shown in the fiure. The nle θ such tht rod remins stble will be. θ () tn () tn 3 (3) tn () tn Ans. () Lets considered mss of ech rod is m for stble equilibrium the torque bout point O should be zero. θ O m m Torque blnce bout O m sinθ m cosθ sinθ tnθ 3 tn 3 PAGE #

12 JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS 3. A rod is cted by two equl forces s shown in the fiure. The coefficient of therml expnsion of the rod is α nd re of cross section is A. When the temperture the rod incresed by t. The lenth of the rod does not chne. The youn's modulus Y will be. Y α, T () () (3) Aα T Aα T Ans. () L Lα T L stress strin α T ; Y L strin Aα T Aα T () 3Aα T. A cpcitor is formed by two squre metl-pltes of ede, seprted by distnce d. Dielectric of dielectric constnts K is filled in the p s shown in the fiure. The equivlent cpcitnce is d K () kε nk d( k ) () kε nk d( k ) (3) kε nk d( k ) () kε nk d( k ) Ans. () Let's consider strip of thickness dx t distnce of x from the left end s shown in the fiure. y d d y x x d y C C K C C eq x dx εdx ; ( d y) CC C + C kε dx kd + ( k)y Now intertin it from to kd + kε dx kε d d ( ) ( k ) k x nk C kεdx y PAGE #

13 JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS 5. In semiconductor mobility of electron, i.e. drift velocity per unit pplied electric field is.6 (S. unit). Density of electron is 9 /m 3. (Nelect holes concentrtion). Resistivity of semi conductor is :- (). Ωm () Ωm (3) Ωm (). Ωm Ans. () σ neµ ρ.ωm neµ A block of mss M is hnin by strin of neliible mss in cr. The speed of wve in the strin 6 m/s. Now cr is ccelerted horizontlly by n ccelertion the speed of wve in the strin is 6.5 m/s. Wht is in terms of? () () (3) () Ans. (3) v + T / µ + M µ usin by binomil pproximtion 6 7. m m/ L/3 L/3 If liht rod is rotted by nle θ nd torque eqution is iven by τ kθ. If rod is rotted by nle θ then the mximum tension in the rod is ( ) 3k θ () Ans. (3) () ( ) k θ (3) k( θ ) () ( ) k θ PAGE #

14 JEE MAIN-9 DATE : 9--9 (SHIT-) PAPER- CONCEPT BASED PHYSICS m m/ Ω ω θ k I T mω T m 3 θ k L/3 L/3 Ω 3 k θ where I m I 3 PAGE # 3