Tiêu đề Work, Energy & Power-1.pdf ✅

CHAPTER WAVES 5 Exercise 1: NCERT Based Topic-wise MCQs 5.1 INTRODUCTION 1. Let A = iˆAcos θ + jˆAsin θ be any vector. Another vector B, which is normal to A can be expressed as (a) iˆBcos θ − ˆjBsin θ NCERT Page-115 / N-72 (b) iˆBcos θ + jˆBsin θ (c) iˆBsin θ − ˆjBcos θ (d) iˆBsin θ + ˆjBcos θ 2. If A⃗ = 4iˆ + 3jˆ and B⃗⃗ = 3iˆ + 4jˆ then cosine of angle between A⃗ and A⃗ + B⃗⃗ is NCERT Page-115 / N-72 (a) 9√2 5 (b) 7 5√2 (c) 5√2 49 (d) 5√2 28 3. A particle moves from position 3iˆ + 2jˆ − 6kˆ to 14iˆ + 13jˆ + 9kˆ due to a uniform force of (4iˆ + jˆ + 3kˆ )N. If the displacement is in metre then work done will be NCERT Page-115 / N-72 (a) 300J (b) 250J (c) 100J (d) 0 4. If a vector 2iˆ + 3jˆ + 8kˆ is perpendicular to the vector 4jˆ − 4iˆ + αkˆ , then the value of α is NCERT Page-115 / N-72 (a) 1/2 (b) −1/2 (c) 1 (d) -1 5.2 NOTIONS OF WORK AND KINETIC ENERGY: THE WORK-ENERGY THEOREM 5. According to work-energy theorem, the work done by the net force on a particle is equal to the change in its (a) kinetic energy NCERT Page-116 / N-73 (c) linear momentum (b) potential energy (d) angular momentum 6. A body starts from rest and acquires a velocity V in time T. The work done on the body in time t will be proportional to (a) V T t NCERT Page-116 / N-73
(b) V 2 T t 2 (c) V 2 T2 t (d) V 2 T2 t 2 5.3 WORK 7. When the force retards the motion of body, the work done is NCERT Page-117 / N-74 (a) zero (b) negative (c) positive (d) Positive or negative depending upon the magnitude of force and displacement 8. A man pushes a wall and fails to displace it, he does NCERT Page-117 / N-74 (a) negative work (b) positive but not maximum work (c) no work at all (d) maximum positive work 9. A boy carrying a box on his head is walking on a level road from one place to another is doing no work. This statement is NCERT Page-117 / N-74 (a) correct (c) partly correct (b) incorrect (d) cannot say 10. No work is done if NCERT Page-117 / N-74 (a) displacement is zero (b) force is zero (c) force and displacement are mutually perpendicular (d) All of these 11. A particle is taken round a circle by application of force. The work done by the force is NCERT Page-117 / N-74 (a) positive non-zero (c) Zero (b) negative non-zero (d) None of these 12. A porter lifts a heavy suitcase of mass 80kg and at the destination lowers it down by a distance of 80cm with a constant velocity. Calculate the work done by the porter in lowering the suitcase. (take g = 9.8ms−2 ) (a) −62720.0J NCERT Page-117 / N-74 (b) −627.2J (c) +627.2J (d) 784.0J 13. Consider a force F⃗ = −xiˆ + yjˆ. The work done by this force in moving a particle from point A(1,0) to B(0,1) along the line segment is: (all quantities are in SI units) NCERT Page-117 / N-74 (a) 2J (b) 1 2 J (c) 1J (d) 3 2 J
14. If W represents the work done, then match the two columns: NCERT/ Page-117 / N-74 COLUMN I COLUMN II (A) Force is always along the velocity (1) W = 0 (B) Force is always perpendicular to velocity (2) W < 0 (C) Force is always perpendicular to acceleration (3) W > 0 (D) The object is stationary but the point of application of the force moves on the object (a) (A) → (1); (B) → (2); C → (3); (D) → (2) (b) (A) → (3); (B) → (1); C → (2,3); (D) → (1) (c) (A) → (2); (B) → (3); C → (1); (D) → (2) (d) (A) → (1); (B) → (2); C → (3); (D) → (1) 15. A particle moving in the xy plane undergoes a displacement of s⃗ = (2iˆ + 3jˆ) while a constant force F⃗ = (5iˆ + 2jˆ)N acts on the particle. The work done by the force F is NCERT Page-117 / N-74 (a) 17 joule (b) 18 joule (c) 16 joule (d) 15 joule 16. A particle describe a horizontal circle of radius 0.5m with uniform speed. The centripetal force acting is 10N. The work done in describing a semicircle is NCERT & Page-117 / N-74 (a) zero (b) 5J (c) 5πJ (d) 10πJ 17. A force acts on a 30g particle in such a way that the position of the particle as a function of time is given by x = 3t − 4t 2 + t 3 , where x is in metres and t is in seconds. The work done during the first 4 seconds is (a) 576mJ NCERT Page-118 / N-74 (b) 450mJ (c) 490mJ (d) 530mJ 18. A cord is used to lower vertically a block of mass M, a distance d at a constant downward acceleration of g/4. The work done by the cord on the block is NCERT Page-118 / N-74 (a) Mg d 4 (b) 3Mg d 4 (c) − 3Mg d 4 (d (d) Mgd 19. If a motorcyclist skids and stops after covering a distance of 15m. The stopping force acting on the motorcycle by the road is 100N, then the work done by the motorcycle on the road is NCERT Page-118 / N-74 (a) 1500J (b) −1500J
(c) 750J (d) Zero 20. A ball moves in a frictionless inclined table without slipping. The work done by the table surface on the ball is (a) positive NCERT Page-118 / N-74 (b) negative (c) zero (d) None of these 21. A uniform force of (3iˆ + jˆ) newton acts on a particle of mass 2kg. The particle is displaced from position (2iˆ + kˆ ) meter to position (4iˆ + 3jˆ − kˆ ) meter. The work done by the force on the particle is NCERT Page-117 / N-74 (a) 6J (b) 13J (c) 15J (d) 9J 22. A boy pushes a toy box 2.0m along the floor by means of a force of 10N directed downward at an angle of 60∘ to the horizontal. The work done by the boy is NCERT Page-117 / N-74 (a) 6J (b) 8J (c) 10J (d) 12J 23. A body moves a distance of 10m along a straight line under the action of a force of 5 newtons. If the work done is 25 joules, the angle which the force makes with the direction of motion of body is NCERT Page-117 / N-74 (a) 0 ∘ (b) 30∘ (c) 60∘ (d) 90∘ 5.4 KINETIC ENERGY 24. A light and a heavy body have equal momentum. Which one has greater K.E.? NCERT Page-117 / N-74 (a) The lighter body (b) The heavier body (c) Both have equal K.E. (d) Data given is incomplete 25. A particle of mass m has momentum p. Its kinetic energy will b NCERT Page-117 / N-74 (a) mp (b) p 2m (c) p 2 m (d) p 2 2m 26. Kinetic energy, with any reference, must be NCERT Page-117 / N-74 (a) zero (b) positive (c) negative (d) both (b) and (c) 27. If the momentum of a body is increased by 50%, then the percentage increase in its kinetic energy is (a) 50% NCERT Page-117 / N-74 (b) 100%