Tiêu đề 05. NEWTONS LAWS OF MOTION EASY.pdf ✅

1. A boy sitting on the topmost berth in the compartment of a train which is just going to stop on a railway station, drops an apple aiming at the open hand of his brother sitting vertically below his hands at a distance of about 2 meter. The apple will fall (a) Precisely on the hand of his brother (b) Slightly away from the hand of his brother in the direction of motion of the train (c) Slightly away from the hand of his brother in the direction opposite to the direction of motion of the train (d) None of the above 2. Newton's first law of motion describes the following (a) Energy (b) Work (c) Inertia (d) Moment of inertia 3. A person sitting in an open car moving at constant velocity throws a ball vertically up into air. The ball falls (a) Outside the car (b)In the car ahead of the person (c) In the car to the side of the person (d)Exactly in the hand which threw it up 4. A bird weighs 2 kg and is inside a closed cage of 1 kg. If it starts flying, then what is the weight of the bird and cage assembly (a) 1.5 kg (b) 2.5 kg (c) 3 kg (d) 4 kg 5. A particle is moving with a constant speed along a straight line path. A force is not required to (a) Increase its speed (b)Decrease the momentum (c) Change the direction (d)Keep it moving with uniform velocity 6. A mass of 1 kg is suspended by a string A. Another string C is connected to its lower end (see figure). If a sudden jerk is given to C, then (a) The portion AB of the string will break (b) The portion BC of the string will break (c) None of the strings will break (d) The mass will start rotating 7. In the above Question, if the string C is stretched slowly, then (a) The portion AB of the string will break (b) The portion BC of the string will break (c) None of the strings will break (d)None of the above 8. If a bullet of mass 5 gm moving with velocity 100 m /sec, penetrates the wooden block up to 6 cm. Then the average force imposed by the bullet on the block is (a) 8300 N (b) 417 N (c) 830 N (d) Zero 9. A force of 100 dynes acts on mass of 5 gm for 10 sec. The velocity produced is (a) 2 cm/sec (b) 20 cm/sec (c) 200 cm/sec (d) 2000 cm/sec 10. An object will continue moving uniformly until (a) The resultant force acting on it begins to decrease (b) The resultant force on it is zero (c) The resultant force is at right angle to its rotation (d) The resultant force on it is increased continuously 11. A diwali rocket is ejecting 0.05 kg of gases per second at a velocity of 400 m/sec. The accelerating force on the rocket is (a) 20 dynes (b) 20 N (c) 22 dynes (d) 1000 N 12. A body of mass 2 kg moving on a horizontal surface with an initial velocity of 4 m/sec comes to rest after 2 sec. If one wants to keep this body moving on the same surface with a velocity of 4 m/sec, the force required is (a) 8 N (b) 4 N (c) Zero (d) 2 N 13. A body of mass 2 kg is hung on a spring balance mounted vertically in a lift. If the lift descends with an acceleration equal to the acceleration due to gravity ‘g’, the reading on the spring balance will be (a) 2 kg (b) (4  g)kg (c) (2  g)kg (d) Zero 14. A coin is dropped in a lift. It takes time 1 t to reach the floor when lift is stationary. It takes time 2 t when lift is moving up with constant acceleration. Then (a) 1 2 t  t (b) 2 1 t  t (c) 1 2 t = t (d) 1 2 t  t 1kg B A C
15. If the tension in the cable of 1000 kg elevator is 1000 kg weight, the elevator (a) Is accelerating upwards (b) Is accelerating downwards (c) May be at rest or accelerating (d)May be at rest or in uniform motion 16. A man weighing 80 kg is standing in a trolley weighing 320 kg. The trolley is resting on frictionless horizontal rails. If the man starts walking on the trolley with a speed of 1 m / s, then after 4 sec his displacement relative to the ground will be (a) 5 m (b) 4.8 m (c) 3.2 m (d) 3.0 m 17. A force of 5 N acts on a body of weight 9.8 N. What is the acceleration produced in 2 m/sec (a) 49.00 (b) 5.00 (c) 1.46 (d) 0.51 18. A body of mass 40 gm is moving with a constant velocity of 2 cm/sec on a horizontal frictionless table. The force on the table is (a) 39200 dyne (b) 160 dyne (c) 80 dyne (d) Zero dyne 19. When 1 N force acts on 1 kg body that is able to move freely, the body receives (a) A speed of 1 m/sec (b) An acceleration of 2 1m / sec (c) An acceleration of 2 980 cm / sec (d) An acceleration of 2 1 cm / sec 20. An object with a mass 10 kg moves at a constant velocity of 10 m/sec. A constant force then acts for 4 second on the object and gives it a speed of 2 m/sec in opposite direction. The acceleration produced in it, is (a) 2 3 m / sec (b) 2 − 3 m / sec (c) 2 0.3 m / sec (d) 2 − 0.3 m / sec 21. A machine gun is mounted on a 2000 kg car on a horizontal frictionless surface. At some instant the gun fires bullets of mass 10 gm with a velocity of 500 m/sec with respect to the car. The number of bullets fired per second is ten. The average thrust on the system is (a) 550 N (b) 50 N (c) 250 N (d) 250 dyne 22. A person is standing in an elevator. In which situation he finds his weight less than actual when (a) The elevator moves upward with constant acceleration (b) The elevator moves downward with constant acceleration. (c) The elevator moves upward with uniform velocity (d) The elevator moves downward with uniform velocity 23. A particle of mass 0.3 kg is subjected to a force F = −kx with k = 15 N / m. What will be its initial acceleration if it is released from a point 20 cm away from the origin (a) 5 m/s2 (b) 10 m/s2 (c) 3 m/s2 (d) 15 m/s2 24. A block of metal weighing 2 kg is resting on a frictionless plane. It is struck by a jet releasing water at a rate of 1 kg/sec and at a speed of 5 m/sec. The initial acceleration of the block will be (a) 2 2.5 m /sec (b) 2 5.0 m /sec (c) 2 10 m /sec (d) None of the above 25. Gravels are dropped on a conveyor belt at the rate of 0.5 kg/sec. The extra force required in newtons to keep the belt moving at 2 m/sec is (a) 1 (b) 2 (c) 4 (d) 0.5 26. A parachutist of weight ‘w’ strikes the ground with his legs fixed and comes to rest with an upward acceleration of magnitude 3 g. Force exerted on him by ground during landing is (a) w (b) 2w (c) 3w (d) 4w 27. At a place where the acceleration due to gravity is 2 10 sec− m a force of 5 kg-wt acts on a body of mass 10 kg initially at rest. The velocity of the body after 4 second is (a) 1 5 sec− m (b) 1 10 sec− m (c) 1 20 sec− m (d) 1 50 sec− m 28. In a rocket of mass 1000 kg fuel is consumed at a rate of 40 kg/s. The velocity of the gases ejected from the rocket is 5 10 m / s 4  . The thrust on the rocket is
(a) N 3 2 10 (b) N 4 5 10 (c) N 6 2 10 (d) N 9 2 10 29. A man is standing on a weighing machine placed in a lift. When stationary his weight is recorded as 40 kg. If the lift is accelerated upwards with an acceleration of 2 2m / s , then the weight recorded in the machine will be ( 10 / ) 2 g = m s (a) 32 kg (b) 40 kg (c) 42 kg (d) 48 kg 30. A body of mass 4 kg weighs 4.8 kg when suspended in a moving lift. The acceleration of the lift is (a) 2 9.80 − ms downwards (b) 9.80 −2 ms upwards (c) 1.96 −2 ms downwards (d) 1.96 −2 ms upwards 31. An elevator weighing 6000 kg is pulled upward by a cable with an acceleration of 2 5 − ms . Taking g to be 2 10 − ms , then the tension in the cable is (a) 6000 N (b) 9000 N (c) 60000 N (d) 90000 N 32. A ball of mass 0.2 kg moves with a velocity of 20 m/sec and it stops in 0.1 sec; then the force on the ball is (a) 40 N (b) 20 N (c) 4 N (d) 2 N 33. A vehicle of 100 kg is moving with a velocity of 5 m/sec. To stop it in sec 10 1 , the required force in opposite direction is (a) 5000 N (b) 500 N (c) 50 N (d) 1000 N 34. A boy having a mass equal to 40 kilograms is standing in an elevator. The force felt by the feet of the boy will be greatest when the elevator ( 9.8 /sec ) 2 g = metres = (a) Stands still (b) Moves downward at a constant velocity of 4 metres/sec (c) Accelerates downward with an acceleration equal to 2 4 metres /sec (d) Accelerates upward with an acceleration equal to 2 4 metres /sec 35. A rocket has an initial mass of kg 3 20 10 . If it is to blast off with an initial acceleration of 2 4 − ms , the initial thrust needed is 10 ) ~ ( −2 g = ms (a) N 4 6 10 (b) N 4 28 10 (c) N 4 20 10 (d) N 4 12 10 36. The ratio of the weight of a man in a stationary lift and when it is moving downward with uniform acceleration ‘a’ is 3 : 2. The value of ‘a’ is (g-Acceleration due to gravity of the earth) (a) g 2 3 (b) 3 g (c) g 3 2 (d) g 37. The mass of a lift is 500 kg. When it ascends with an acceleration of 2 2m / s , the tension in the cable will be [ 10 / ] 2 g = m s (a) 6000 N (b) 5000 N (c) 4000 N (d) 50 N 38. If force on a rocket having exhaust velocity of 300 m/sec is 210 N, then rate of combustion of the fuel is (a) 0.7 kg/s (b) 1.4 kg/s (c) 0.07 kg/s (d) 10.7 kg/s 39. In an elevator moving vertically up with an acceleration g, the force exerted on the floor by a passenger of mass M is (a) Mg (b) Mg 2 1 (c) Zero (d) 2 Mg 40. A mass 1 kg is suspended by a thread. It is (i) lifted up with an acceleration 2 4.9 m /s (ii) lowered with an acceleration 2 4.9 m /s . The ratio of the tensions is (a) 3 : 1 (b) 1 : 3 (c) 1 : 2 (d) 2 : 1 41. A 5000 kg rocket is set for vertical firing. The exhaust speed is 1 800 − ms . To give an initial upward acceleration of 2 20 − ms , the amount of gas ejected per second to supply the needed thrust will be ( 10 ) −2 g = ms (a) 1 127 .5 − kg s (b) 1 187 .5 − kg s (c) 1 185 .5 − kg s (d) 1 137 .5 − kg s
42. If a person with a spring balance and a body hanging from it goes up and up in an aeroplane, then the reading of the weight of the body as indicated by the spring balance will (a) Go on increasing (b)Go on decreasing (c) First increase and then decrease (d)Remain the same 43. The time period of a simple pendulum measured inside a stationary lift is found to be T. If the lift starts accelerating upwards with an acceleration g/3, the time period is (a) T 3 (b) T 3 / 2 (c) T / 3 (d) T / 3 44. A cork is submerged in water by a spring attached to the bottom of a pail. When the pail is kept in a elevator moving with an acceleration downwards, the spring length (a) Increases (b) Decreases (c) Remains unchanged (d) Data insufficient 45. Two trolleys of mass m and 3m are connected by a spring. They were compressed and released once, they move off in opposite direction and comes to rest after covering distances 1 S and 2 S respectively. Assuming the coefficient of friction to be uniform, the ratio of distances 1 2 S : S is (a) 1 : 9 (b) 1 : 3 (c) 3 : 1 (d) 9 : 1 46. A boy of 50 kg is in a lift moving down with an acceleration 2 9.8 − ms . The apparent weight of the body is ( 9.8 ) −2 g = ms (a) 50  9.8 N (b) Zero (c) 50 N (d) N 9.8 50 47. A body is imparted motion from rest to move in a straight line. If it is then obstructed by an opposite force, then (a) The body may necessarily change direction (b) The body is sure to slow down (c) The body will necessarily continue to move in the same direction at the same speed (d) None of these 48. A mass of 10 gm is suspended by a string and the entire system is falling with a uniform acceleration of 400 /sec . 2 cm The tension in the string will be ( 980 /sec ) 2 g = cm (a) 5,800 dyne (b) 9,800 dyne (c) 11,800 dyne (d) 13,800 dyne 49. A second's pendulum is mounted in a rocket. Its period of oscillation decreases when the rocket (a) Comes down with uniform acceleration (b) Moves round the earth in a geostationary orbit (c) Moves up with a uniform velocity (d) Moves up with uniform acceleration 50. Two balls of masses m1 and m2 are separated from each other by a powder charge placed between them. The whole system is at rest on the ground. Suddenly the powder charge explodes and masses are pushed apart. The mass m1 travels a distance 1 s and stops. If the coefficients of friction between the balls and ground are same, the mass m2 stops after travelling the distance (a) 1 2 1 2 s m m s = (b) 1 1 2 2 s m m s = (c) 2 1 2 2 1 2 s m m s = (d) 2 1 1 2 2 2 s m m s = 51. A force vector applied on a mass is represented as F i j k ˆ 10 ˆ 8 ˆ = 6 − +  and accelerates with 2 1m / s . What will be the mass of the body (a) 10 2 kg (b) 2 10 kg (c) 10 kg (d) 20 kg 52. A cart of mass M is tied by one end of a massless rope of length 10 m. The other end of the rope is in the hands of a man of mass M. The entire system is on a smooth horizontal surface. The man is at x = 0 and the cart at x = 10 m. If the man pulls the cart by the rope, the man and the cart will meet at the point (a) x = 0 (b) x = 5 m (c) x = 10 m (d) They will never meet 53. A cricket ball of mass 250 g collides with a bat with velocity 10 m/s and returns with the same velocity within