Tiêu đề WORK ENERGY & POWER.pdf ✅

NEET : Physics [306] www.allendigital.in  Digital WORK 1. A force ( ) ˆ ˆ ˆ F 4i 4j 2k N = − − displaces a particle by ( ) ˆ ˆ ˆ d 3i 2j 2k m = + − , calculate work done. (1) Zero (2) 8 J (3) 4 J (4) 12 J 2. A force ( ) F 3i 2j N = + ˆ ˆ acts on a body and produces a displacement ( ) ˆ ˆ ˆ S 4i j 3k m = − + . The work done will be (1) 13 J (2) 30 J (3) 10 J (4) 20 J 3. A particle is moved from a position 1 ˆ ˆ ˆ r (2i j 2k) = + − metre to a position 2 ˆ ˆ ˆ r (4i 3j k) = + − metre under the action of a force ˆ ˆ ˆ F (3i 2j 2k) = + + N. The work done is equal to :- (1) 32 J (2) 12 J (3) 24 J (4) 16 J 4. A body of mass m is displaced from point A(3, 1, 3) m to point B(1, 2, 1) m under the effect of a force ˆ ˆ ˆ F (3i 2j 2k) = + + , calculate work done by the force. (1) 57 J (2) 11 J (3) 0 (4) 22 J 5. A person of mass m is standing on one end of a plank of mass M and length L floating in water. The person moves from one end to another and stops. Work done by normal force is – (1) MgL (2) mgL (3) mMgL M m+ (4) 0 6. The work done against gravity in taking 5 kg. mass to 2 m height in 1 s will be :- (1) 49 J (2) 98 J (3) 196 J (4) None of these 7. A stone of mass m is tied to a string of length  at one end and by holding second end it is whirled into a horizontal circle with constant speed v, then work done by the string on the stone will be :– (1) 0 (2) 2 mv 2        (3) (mg)·2 (4) 2   mv     8. A student of Allen is going from samarth to sabal building holding his bag in his hand. Direct distance between these buildings is 50m. Calculate work done by gravity if mass of bag is 3 kg. (1) 750 J (2) 1500 J (3) Zero (4) Data insufficient 9. You lift a heavy book from the floor of the room and keep it in the book–shelf having a height 2 m. In this process you take 5 seconds. The work done by you will depend upon :- (1) Mass of the book and time taken. (2) Weight of the book and height of the book-shelf (3) Height of the book-shelf and time taken. (4) Mass of the book, height of the book-shelf and time taken. 10. Work done by static friction is : (1) Always zero (2) Always non-zero (3) May be zero or non-zero (4) None of these 11. For the system shown in figure both the block A and B are moving together. If coefficient of friction between both the blocks is μ, the work done by friction on block B is :- (1) Zero (2) Negative (3) Positive (4) None of these 12. A body of mass M tied to a string is lowered at a constant acceleration of (3g/4) through a vertical distance h. The work done by the string will be.............. (1) 3 4 Mgh (2) 1 4 Mgh (3) 3 4 − Mgh (4) 1 4 − Mgh smooth μ A F B Exercise - I

NEET : Physics [308] www.allendigital.in  Digital 22. Figure gives the acceleration of a 4.0 kg body as it moves from rest along x axis while a variable force acts on it from x = 0m to x = 9m. The work done by the force on the body when it reaches (i) x = 4m and (ii) x = 7 m shall be as given below (1) 21 J and 33 J respectively (2) 21 J and 15 J respectively (3) 42 J and 60 J respectively (4) 42 J and 30 J respectively 23. Calculate the work done for following F-d curves (A) (P) 30 J (B) (Q) 140 J (C) (R) 45 J (D) (1) (A - R); (B - Q); (C - P); (D - R) (2) (A - R); (B - P); (C - R); (D - Q) (3) (A - R); (B - P); (C - Q); (D - R) (4) (A - P); (B - Q); (C - R); (D - P) KINETIC ENERGY & WORK ENERGY THEOREM 24. The kinetic energy of a body becomes nine times of its initial value. The new linear momentum will be :- (1) Four times the initial value (2) Thrice the initial value (3) Twice the initial value (4) Same as the initial value 25. If the momentum of a body is increased n times, its kinetic energy increases. (1) n times (2) 2n times (3) n times (4) n2 times 26. If the kinetic energy of a body becomes 4 times of its initial kinetic energy, then the momentum of the body will become :- (1) 2 2 times (2) 2 times (3) 2 times (4) none of these 27. Two bodies of mass 4kg and 9kg have equal K.E. then the ratio of their momentum is :- (1) 3 : 2 (2) 2 : 3 (3) 4 : 9 (4) 16 : 8 28. 2 particles of mass 3 Kg and 5 kg have same momentum, calculate ratio of their K.E. (1) 5 : 3 (2) 3 : 5 (3) 25 : 9 (4) 9 : 25 29. If K.E. of body is increased by 300%. Then % change in its 'P' will be (1) 100% (2) 41.4% (3) 17.3% (4) 200% 30. If the kinetic energy of a body is increased by 800%, the momentum will increase by :- (1) 100% (2) 200% (3) 150% (4) 300% 31. If K.E. of a body increases by 3%, then momentum will increase by :- (1) 1.5% (2) 9% (3) 3% (4) 2% 32. If the momentum of a body increases by 2% then it's kinetic energy :- (1) increases by 2% (2) increases by 4% (3) increases by 8% (4) increases by 16% 0 3 –3 x(m) a (m/s 2 4 6 8 2)  F(N) 70 –30 2 3 5 d(m) → 20 15 5 –15 1 3 4 5 6  F(N) d(m) → 25 15 1 2 3 4 5 –15 d(m) →  F(N) 5 10 15 2 4 d(m) →  F(N) 0
Work, Energy and Power  Digital www.allendigital.in [309] 33. The graph between k E and 1 p is (EK = kinetic energy and p = momentum) – (1) (2) (3) (4) 34. The graph between kinetic energy EK and velocity V is – (1) (2) (3) (4) 35. A constant force F is applied to a body of mass m moving with initial velocity u. If after the body undergoes a displacement S, its velocity becomes v, then the total work done is :- (1) m[v2 + u2] (2) m 2 [u2 + v2] (3) m 2 [v2 – u2] (4) m[v2 – u2] 36. A body of mass 6 kg is acted upon by a force which causes displacement in it given as S = 3 t 4 metres where ‘t’ is time. The work done by the force in 2 seconds is :- (1) 18 J (2) 9 J (3) 27 J (4) 16 J 37. A force acts on a 20 g particle in such a way that the position of the particle as a function of time is given by x = 2t – 3t2 + 2t3, where x is in metre and t is in second. The work done during the first 3 second is :- (1) 5.28 J (2) 28.8 J (3) 14.4 J (4) 7.2 J 38. A ball of mass 1 kg and another of mass 3 kg are dropped together from a 60 feet tall building. After a fall of 30 feet each towards earth, their respective kinetic energies will be in the ratio of :- (1) 1 : 3 (2) 1 : 2 (3) 1 : 3 (4) 3 : 1 39. A 2 kg ball is thrown up with an initial speed 16 m/s and reaches a maximum height of 10 m. How much energy is dissipated by air drag acting on the ball during the ascent ? (1) 40 J (2) 56 J (3) 36 J (4) 72 J 40. Three particles A, B and C are projected from the top of a tower with the same speed. A is thrown straight upwards, B straight down and C horizontally. They hit the ground with speeds VA, VB and VC then: (1) VA = VB > VC (2) VA = VB = VC (3) VA > VB = VC (4) VB > VC > VA 41. Velocity–time graph of a particle of mass 2 kg moving in a straight line is as shown in figure. Work done by all the forces acting on the particle is : (1) 100 J (2) –100 J (3) –200 J (4) 200 J CONSERVATIVE FORCE & POTENTIAL ENERGY 42. Which of the following statements is not true for work done by conservative forces :– (1) It does not depend on path (2) It is equal to the difference of initial and final potential energy function (3) It can be recovered completely (4) None of the above 43. Which of the following statement is incorrect for a conservative field ? (1) Work done in going from initial to final position is equal to change in kinetic energy of the particle. (2) Work done depends on path but not on initial and final positions. (3) Work done does not depend on path but depends only on initial and final positions (4) Work done on a particle in the field for a round trip is zero. Ek 1/p Ek 1/p Ek 1/p Ek 1/p Ek V Ek V V Ek Ek V 2 10 v (m/s) t (s)