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Page 1 1. (d) 90 2 sin 2 vv ° æö D= ç÷ èø 1 2sin4522 2 v vv = °= ´= 22 2 21 60 30 pp =´w=´´ = r cm/s 2. (b) 2 sin 2 vv q æö D= ç÷ èø 10 2 5 sin 45 2 = ´ ´ °= \ v a t D = D 10/21 10 2 == m/s 2 3. (c) For motion of the particle from (0, 0) to (a, 0) $ ˆˆ (0) FKi aj FKaj =- + Þ =- ur ur Displacement ˆˆ ˆˆ ( 0) (0 0) r ai j i j ai = + - += r $ So work done from (0, 0) to (a, 0) is given by $ . .0 W F r Ka j ai = =-= urr $ For motion (a, 0) to (a, a) $ () F K ai aj =-+ ur $ and displacement $ ˆ ˆ ˆˆ ( ) ( 0) r ai aj ai j a j = + - += r So work done from (a, 0) to (a, a) $ $ 2 . ( ). urr $ W F r K ai a j a j Ka = =- + =- So total work done = 2 Ka - 4. (d) q W P T sin T q cos T q As the metal sphere is in equilibrium under the effect of the three forces therefore 0 T PW + += ururuur From the figure cos TW q= ................... (i) sin TP q= ................... (ii) From equation (i) and (ii) we get tan PW =q and 2 22 T PW =+ 5. (b) Time taken to cross the river along shortest possible path is given by 22 = - d t vu v = velocity of boat in still water u = velocity of river water d = width of river 22 151 60 5 \= -u Þ u = 3 km/h 6. (d) Here d = 320 m = 320 km 1000 t = 4 min v = 5 3 u Putting values in 22 = - d t vu , u = 60 m/min 7. (c) 12 sin sin sin150 P QR == q q° Þ 1 1.93 sin sin150 R = q° Þ 1 1.93 sin150 1.93 0.5 1 sin 0.9659 R ´ °´ = == q P Q R 150° 2 q 1 q 8. (b) T T cos 30° T sin 30° 30 N W 30° Page 2 1. (d) 90 2 sin 2 vv ° æö D= ç÷ èø 1 2sin4522 2 v vv = °= ´= 22 2 21 60 30 pp =´w=´´ = r cm/s 2. (b) 2 sin 2 vv q æö D= ç÷ èø 10 2 5 sin 45 2 = ´ ´ °= \ v a t D = D 10/21 10 2 == m/s 2 3. (c) For motion of the particle from (0, 0) to (a, 0) $ ˆˆ (0) FKi aj FKaj =- + Þ =- ur ur Displacement ˆˆ ˆˆ ( 0) (0 0) r ai j i j ai = + - += r $ So work done from (0, 0) to (a, 0) is given by $ . .0 W F r Ka j ai = =-= urr $ For motion (a, 0) to (a, a) $ () F K ai aj =-+ ur $ and displacement $ ˆ ˆ ˆˆ ( ) ( 0) r ai aj ai j a j = + - += r So work done from (a, 0) to (a, a) $ $ 2 . ( ). urr $ W F r K ai a j a j Ka = =- + =- So total work done = 2 Ka - 4. (d) q W P T sin T q cos T q As the metal sphere is in equilibrium under the effect of the three forces therefore 0 T PW + += ururuur From the figure cos TW q= ................... (i) sin TP q= ................... (ii) From equation (i) and (ii) we get tan PW =q and 2 22 T PW =+ 5. (b) Time taken to cross the river along shortest possible path is given by 22 = - d t vu v = velocity of boat in still water u = velocity of river water d = width of river 22 151 60 5 \= -u Þ u = 3 km/h 6. (d) Here d = 320 m = 320 km 1000 t = 4 min v = 5 3 u Putting values in 22 = - d t vu , u = 60 m/min 7. (c) 12 sin sin sin150 P QR == q q° Þ 1 1.93 sin sin150 R = q° Þ 1 1.93 sin150 1.93 0.5 1 sin 0.9659 R ´ °´ = == q P Q R 150° 2 q 1 q 8. (b) T T cos 30° T sin 30° 30 N W 30° 12 DPP/ P 05 From the figure T sin 30° = 30 ...(i) T cos 30° = W ...(ii) By solving equation (i) and (ii) we get 303 WN = and T = 60 N 9. (c) Relative velocity = ˆˆ ˆˆ ˆ ˆ (3 4) (34) 68 i j i j ij + -- - =+ 10. (c) 30° 90° m v r v sin 30° = 1 2 r m v v = Þ 0.5 0.25 22 m r v v= == m/s 11. (a) To cross the river in minimum time, the shift is given by du v . 12. (d) Relative velocity = 10 + 5 = 15 m/s. Time taken by the bird to cross the train = 120 8 15 = sec 13. (d) vr = w´ r urr $ $ $ $ 3 4 1 18 13 2 5 66 i jk i jk = - =- -+ - $ $ 14. (d) | | 3( .) ur u r ur ur A B AB ´= sin 3 cos AB AB q=q Þtan3 q= Þ 60 q=° Now |||| R AB =+ ur ur ur 22 2 cos A B AB = ++q 22 1 2 2 A B AB æö = ++ ç÷ èø = 2 2 1/2 () A B AB ++ 15. (a) $ $ $ $ (7 3 )( 3 5) r F i j k i jk t= ´ = + + - ++ r r ur $$ $ $ $ $ 7 3 1 14 38 16 3 15 i jk i jk t= = -+ - $ r $ 16. (b)| |. ur ur ur ur B AB A´= Þ sin cos AB AB q=q Þ tan1 q= \ 45 q=° 17. (a) .0 PQ = u r ur Þ 2 2 30 aa - -= Þ a = 3 18. (a) 21 u u r ur r S rr =- . W FS = ur ur = $ $ $ $ (4 3).(11 11 15) i j k i jk + + ++ $$ = (4 × 11 + 1 × 11 + 3 × 15) = 100 J 19. (c) ˆˆ ˆ ˆ ˆˆ 3 2 , 35 A i j kB i jk = - + = -+ u r ur , ˆ ˆˆ 24 C i jk = +- ur 2 22 3 ( 2) 1 9 4 1 14 A = + - + = + += r 2 22 1 ( 3) 5 1 9 25 35 B= +- += + += r 222 2 1 ( 4) 4 1 16 21 r C= + +- = ++= As 22 B AC =+ therefore ABC will be right angled triangle. 20. (b) 12 12 . cos FF FF q= rr = ˆˆ ˆ ˆ ˆˆ (5 10 20 ).(10 5 15 ) 25 100 400. 100 25 225 i j k i jk + - -- + + ++ 50 50 300 525. 350 -+ = Þ 1 cos 2 q= 45 \q=° 21. (a) ˆˆ ˆˆ ˆ ˆ ˆˆ 4 32 r abc i j i jk i jk = + + = -- + - = +- r rrr 222 ˆ ˆˆ ˆ || 1 1 ( 1) r i jk r r r +- == + +- ˆ ˆˆ 3 i jk +- = 22. (a) D C A B 300 m 400 m Displacement AC AB BC =+ uuu r uuu r u uu r Page 3 1. (d) 90 2 sin 2 vv ° æö D= ç÷ èø 1 2sin4522 2 v vv = °= ´= 22 2 21 60 30 pp =´w=´´ = r cm/s 2. (b) 2 sin 2 vv q æö D= ç÷ èø 10 2 5 sin 45 2 = ´ ´ °= \ v a t D = D 10/21 10 2 == m/s 2 3. (c) For motion of the particle from (0, 0) to (a, 0) $ ˆˆ (0) FKi aj FKaj =- + Þ =- ur ur Displacement ˆˆ ˆˆ ( 0) (0 0) r ai j i j ai = + - += r $ So work done from (0, 0) to (a, 0) is given by $ . .0 W F r Ka j ai = =-= urr $ For motion (a, 0) to (a, a) $ () F K ai aj =-+ ur $ and displacement $ ˆ ˆ ˆˆ ( ) ( 0) r ai aj ai j a j = + - += r So work done from (a, 0) to (a, a) $ $ 2 . ( ). urr $ W F r K ai a j a j Ka = =- + =- So total work done = 2 Ka - 4. (d) q W P T sin T q cos T q As the metal sphere is in equilibrium under the effect of the three forces therefore 0 T PW + += ururuur From the figure cos TW q= ................... (i) sin TP q= ................... (ii) From equation (i) and (ii) we get tan PW =q and 2 22 T PW =+ 5. (b) Time taken to cross the river along shortest possible path is given by 22 = - d t vu v = velocity of boat in still water u = velocity of river water d = width of river 22 151 60 5 \= -u Þ u = 3 km/h 6. (d) Here d = 320 m = 320 km 1000 t = 4 min v = 5 3 u Putting values in 22 = - d t vu , u = 60 m/min 7. (c) 12 sin sin sin150 P QR == q q° Þ 1 1.93 sin sin150 R = q° Þ 1 1.93 sin150 1.93 0.5 1 sin 0.9659 R ´ °´ = == q P Q R 150° 2 q 1 q 8. (b) T T cos 30° T sin 30° 30 N W 30° 12 DPP/ P 05 From the figure T sin 30° = 30 ...(i) T cos 30° = W ...(ii) By solving equation (i) and (ii) we get 303 WN = and T = 60 N 9. (c) Relative velocity = ˆˆ ˆˆ ˆ ˆ (3 4) (34) 68 i j i j ij + -- - =+ 10. (c) 30° 90° m v r v sin 30° = 1 2 r m v v = Þ 0.5 0.25 22 m r v v= == m/s 11. (a) To cross the river in minimum time, the shift is given by du v . 12. (d) Relative velocity = 10 + 5 = 15 m/s. Time taken by the bird to cross the train = 120 8 15 = sec 13. (d) vr = w´ r urr $ $ $ $ 3 4 1 18 13 2 5 66 i jk i jk = - =- -+ - $ $ 14. (d) | | 3( .) ur u r ur ur A B AB ´= sin 3 cos AB AB q=q Þtan3 q= Þ 60 q=° Now |||| R AB =+ ur ur ur 22 2 cos A B AB = ++q 22 1 2 2 A B AB æö = ++ ç÷ èø = 2 2 1/2 () A B AB ++ 15. (a) $ $ $ $ (7 3 )( 3 5) r F i j k i jk t= ´ = + + - ++ r r ur $$ $ $ $ $ 7 3 1 14 38 16 3 15 i jk i jk t= = -+ - $ r $ 16. (b)| |. ur ur ur ur B AB A´= Þ sin cos AB AB q=q Þ tan1 q= \ 45 q=° 17. (a) .0 PQ = u r ur Þ 2 2 30 aa - -= Þ a = 3 18. (a) 21 u u r ur r S rr =- . W FS = ur ur = $ $ $ $ (4 3).(11 11 15) i j k i jk + + ++ $$ = (4 × 11 + 1 × 11 + 3 × 15) = 100 J 19. (c) ˆˆ ˆ ˆ ˆˆ 3 2 , 35 A i j kB i jk = - + = -+ u r ur , ˆ ˆˆ 24 C i jk = +- ur 2 22 3 ( 2) 1 9 4 1 14 A = + - + = + += r 2 22 1 ( 3) 5 1 9 25 35 B= +- += + += r 222 2 1 ( 4) 4 1 16 21 r C= + +- = ++= As 22 B AC =+ therefore ABC will be right angled triangle. 20. (b) 12 12 . cos FF FF q= rr = ˆˆ ˆ ˆ ˆˆ (5 10 20 ).(10 5 15 ) 25 100 400. 100 25 225 i j k i jk + - -- + + ++ 50 50 300 525. 350 -+ = Þ 1 cos 2 q= 45 \q=° 21. (a) ˆˆ ˆˆ ˆ ˆ ˆˆ 4 32 r abc i j i jk i jk = + + = -- + - = +- r rrr 222 ˆ ˆˆ ˆ || 1 1 ( 1) r i jk r r r +- == + +- ˆ ˆˆ 3 i jk +- = 22. (a) D C A B 300 m 400 m Displacement AC AB BC =+ uuu r uuu r u uu r DPP/ P 05 13 AC = 2 2 22 (AB) (BC) (400) (300) 500m + = += Distance = AB+BC =400+300=700 m 23. (a) ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆˆ A 3i 2j k,B i 3j 5k,C 2i j 4k = - + = - + = -+ rr r 2 22 A 3 ( 2) 1 9 4 1 14 = + - + = + += r 2 22 B 1 ( 3) 5 1 9 25 35 = +-+= + + = r 222 C 2 1 ( 4) 4 1 16 21 = + +- = ++= uv As 22 B AC =+ therefore ABC will be right angled triangle. 24. (a)AB0sin 00 ´ = \ q= \q= ° r r Two vectors will be parallel to each other. 25. (a), 26 (b), 27. (b) ˆ ˆˆ 2 11 1 11 r r i jk AB ´= = ˆ ˆˆ ( 1 1) (2 1) (2 1) i jk -- -+ - = ˆ ˆ jk -+ Unit vector perpendicular to A r and B r is ˆ ˆ 2 jk æö -+ ç÷ èø . Any vector whose magnitude is k (constant) times ˆ ˆˆ (2) i jk ++ is parallel to A r so, unit vector ˆ ˆˆ 2 6 i jk ++ is parallel to A r . 28. (b) A B AB + =- rr rr Þ A 2 + B 2 + 2AB cosq = A 2 + B 2 + 2AB cosq Hence cos q = 0 which gives q = 90° Also vector addition is commutative. Hence A B BA +=+ rr rr 29. (a) Let P r and Q r are two vectors in opposite direction, then their sum () P Q PQ +- =- rr rr If PQ = r r then sum equal to zero. 30. (d) The resultant of two vectors of unequal magnitude given by 22 2 cos R A B AB = ++q cannot be zero for any value of q.Read More
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