Important Questions for competitive exams - Physics

Important Questions for competitive exams (Physics)
1. A vehicle covers the first half of the distance between two places at a speed of 40 km/h and the other half at 60 km/h. The average speed of the vehicle is
   (1) 40 km/h
   (2) 60 km/h
   (3) 50 km/h
   (4) 48 km/h ✔
2. A ball is dropped from a bridge 125 m high. After the ball has been falling for 2 second, another ball is thrown downwards with such a velocity that the two balls strike the surface of water simultaneously. The velocity of the second ball is nearly :
   (1) 27 m/s ✔
   (2) 30 m/s
   (3) 40 m/s
   (4) infinite
3. A stone is thrown vertically upwards from a bridge with a velocity of 4.9 m/s. It strikes water after 2 second. The height of the bridge is :
   (1) 4.9 × 2 m ✔
   (2) 4.9 × 3 m
   (3) 4.9 × 4 m
   (4) 4.9 × 3 × 7 m
4. The displacement x of a body varies with time t as
           x = - ⅔t² + 16t + 2
In what time the body comes to rest?  x is measured in metre and t in second.
   (1) 6 s
   (2) 12 s ✔
   (3) 18 s
   (4) 20 s
5. A train 200 m long passes over a bridge 600 m long. In what time the train will cross the bridge while moving with uniform speed of 36 km/h ?
   (1) 80 s ✔
   (2) 100 s
   (3) 120 s
   (4) 140 s
6. The distance covered by a body is given by 
                   S = at + bt²
The acceleration of the body is
   (1) a/b
   (2) 2b ✔
   (3) a + b
   (4) 3b
7. A car leaves station X for station Y every 10 minutes. The distance between X and Y is 60 km. The speed of each car is 60 km/h. A man drives a car from Y towards X at a speed of 60 km/h. If he starts simultaneously with one of the car from X, how many cars would he meet on the way?
   (1) 5
   (2) 6
   (3) 11 ✔
   (4) 12
8. Starting from rest at the top of the inclined plane, a body reaches the bottom of the inclined plane in 4 second. In what time does the body cover one fourth the distance starting from the rest at the top?
   (1) 1 s
   (2) 2 s ✔
   (3) 3 s
   (4) 4 s
9. A body having uniform acceleration of 10 m/s² has a velocity of 100 m/s. In what time, the velocity will be doubled?
   (1) 8 s
   (2) 10 s ✔
   (3) 12 s
   (4) 14 s
10. If the velocity time graph of a particle is represented by y = mx + c, then the particle is moving with
   (1) constant speed
   (2) constant velocity
   (3) variable velocity ✔
   (4) constant momentum
11. A body is thrown vertically upwards with a speed of 100 m/s . On the return journey, the speed in m/s at the starting point will be
   (1) 100 m/s. ✔
   (2) 9.8 m/s
   (3) 100×9.8 m/s
   (4) 100/9.8 m/s
12. The velocity of a moving particle A with respect to another moving particle B is obtained by compounding the velocity of A with a velocity
   (1) equal (in magnitude) and opposite to that of B  ✔
   (2) equal to that of A
   (3) equal to that of B
   (4) equal and opposite to that of A
13. The co-ordinates, at any time t, of a moving body are given by x = ct² and y = bt².
 The speed of the body is :
   (1) ct²
   (2) bt²
   (3) c/b
   (4) 2t√(b² + c²) ✔
14. A ball is thrown vertically upwards from the surface of Earth with a speed of 18 km/h. If g = 10 m/s² , then the maximum height attained by the ball is :
   (1) 1.25 my  ✔
   (2) 3 m
   (3) 10 m
   (4) 180 m
15. When released from a height of 100 m, a ball falls 5 m in 1 second. In 4 second after release, it falls
   (1) 80 m ✔
   (2) 800 m
   (3) 750 m
   (4) 700 m
16. A car travels 100 km east and then 100 km south. Finally, it comes back to the starting point by the shortest route. Throughout the journey, the speed is constant at 60 km/h. The average velocity for the whole of the journey is
   (1) 60 km/h
   (2) 90 km/h
   (3) 0 km/h ✔
   (4) 180 km/h
17. There is an argument about uniform acceleration between Mr. X and Mr. Y . Mr. X says, "acceleration means that farther you go, faster you go ". Mr. Y says, "acceleration means that longer you go, the faster you go ". Whose statement is correct?
   (1) Mr. X
   (2) Mr. Y
   (3) Both ✔
   (4) None
18. A pendulum is suspended from the roof of a train moving with acceleration 49 cm/s². Then the angle made by the string with the vertical is
   (1) 3° nearly ✔
   (2) 5° nearly
   (3) 7° nearly
   (4) 9° nearly
19. A monkey is at rest on a weightless rope which goes over a pulley and is tied to a bunch of bananas at the other end. The bunch of bananas weighs exactly the same as the monkey. The pulley may be assumed to be frictionless and massless. The monkey starts to climb up the rope to reach bananas. As he climbs, the vertical distance between the monkey and the bananas
   (1) decreases
   (2) increases
   (3) remains unchanged ✔
   (4) first increases and then decreases.
20. A ball falls freely from rest. The ratio of the distances travelled in first, second, third and fourth seconds is :
   (1) 1 : 1 : 1 : 2
   (2) 1 : 1 : 1 : 3
   (3) 1 : 2 : 3 : 4
   (4) 1 : 3 : 5 : 7 ✔
21. A train is moving east at a speed of 5 m/s. A bullet fired westwards with a velocity of 10 m/s crosses the train in 8 s. The length of the train is :
   (1) 120 m ✔
   (2) 60 m
   (3) 30 m
   (4) 15 m
22. A cricket ball and a tennis ball are simultaneously thrown upwards with equal initial speeds. Ignoring air resistance, which of the following statement is correct?
   (1) Both the balls travel the same distance in the same time. ✔
   (2) Tennis ball rises the highest.
   (3) Tennis ball has a smaller impact speed.
   (4) Both the balls have equal potential energy at maximum height.
23. The magnitude of the acceleration of a moving object is equal to the
   (1) gradient of a displacement time graph
   (2) gradient of a velocity time graph ✔
   (3) area below a force time graph
   (4) area below a displacement time graph
24. A stone is thrown vertically upwards with an initial velocity of 30 m/s. The time taken for the stone to rise to its maximum height is
   (1) 0.326 s
   (2) 3.26 s
   (3) 30.6 s
   (4) 3.06 s  ✔
25. From a 200 m high tower, one ball is thrown upwards with a speed of 10 m/s and another is thrown vertically downwards at the same speed simultaneously. The time difference of their reaching the ground will be nearest to :
   (1) 12 s
   (2) 6 s
   (3) 2 s  ✔
   (4) 1 s
26. An elevator car, whose floor to ceiling distance is equal to 2.7 m starts ascending with uniform acceleration of 1.20 m/s². Two second after the start, a bolt begins to fall from the ceiling. What is the free fall time of the bolt?  Given : get = 9.8 m/s².
   (1) 0.7 s
   (2) 1 s ✔
   (3) √0.45 s
   (4) √6 s
27. A ball is thrown upwards. After it has left the hand, its acceleration
   (1) remains constant ✔
   (2) increases
   (3) decreases
   (4) is zero
28. A train travels between two stations 18 km apart in 18 minutes. The train accelerates from rest during the first six minutes and then decelerates during the next 12 minutes before coming to rest. The maximum speed attained in the course of its motion is :
   (1) 60 km/h
   (2) 80 km/h
   (3) 90 km/h
   (4) 120 km/h ✔
29. A bird flies with a speed of 10 km/h and a car moves with uniform speed of 8 km/h. Both starts from B towards A (BA = 40 km) at the same instant. The bird having reached A, flies back immediately to meet the approaching car. As soon as it reaches the car, it flies back to A. The bird repeats this till both the car and the bird reach A simultaneously. The total distance flown by the bird is :
   (1) 80 km
   (2) 40 km
   (3) 50 km ✔
   (4) cannot be determined
30. A body released from a great height falls freely towards the earth. Another body is released from the same height exactly one second later. The separation between the two bodies two second after the release of the second body is :
   (1) 9.8 m
   (2) 4.9 m
   (3) 24.5 m  ✔
   (4) 19.6 m
31. A bus begins to move with an acceleration of 1 m/s². A boy who wants to board it can run at 8 m/s². If the boy just catches the bus, how far was the boy behind the bus when the bus began to move?
   (1) 8 m
   (2) 16 m
   (3) 32 m  ✔
   (4) 48 m
32. The average normal temperature of the human body is
   (1) 98.4° C
   (2) 18.6° C
   (3) 37 ° C ✔
   (4) 20° C
33. A constant volume gas thermometer works on
   (1) Charles' law ✔
   (2) Boyle's law
   (3) the Archimedes' Principle
   (4) Pascal's law
34. Which of the following temperature is the highest?
   (1) 100 K
   (2) — 13° F
   (3) — 20° C ✔
   (4) — 23° C
35. A faulty thermometer has its fixed points marked 5° and 95°. This thermometer reads the temperature of a body as 59°. Then correct temperature on Celsius scale is :
   (1) 59°
   (2) 48.6°
   (3) 60° ✔
   (4) 58°
36. At what temperature, the Fahrenheit and Celsius scales will give numerically equal (but opposite in sign) values
   (1) – 40° F and 40° C
   (2) 11.43° F and – 11.43° C ✔
   (3) – 11.43° F and + 11.43° C
   (4) + 40° F and – 40° C
37. When a copper ball is heated, the largest percentage increase will be in its :
   (1) radius
   (2) volume ✔
   (3) area
   (4) mass
38. A ring-shaped metal is allowed to expand by heating it. The hole will
   (1) expand ✔
   (2) contract
   (3) expand or contract depending upon the width of ring
   (4) expand or contract depending upon the value of coefficient of expansion
39. Bimetal strips are used in
   (1) metal thermometers
   (2) relays for opening or closing electrical circuits
   (3) thermostats
   (4) all of these  ✔
40. A waterfall is 84 m high. Assuming that half the kinetic energy of falling water get converted to heat, the rise in temperature of water is :
   (1) 0.098° C ✔
   (2) 0.98° C
   (3) 98° C
   (4) 0.0098° C
41. The temperature at the bottom of a high waterfall is higher than that at the top because
   (1) by itself heat flows from higher to lower temperature
   (2) the difference in height causes a difference in pressure
   (3) thermal energy is transformed into mechanical energy
   (4) mechanical energy is transformed into thermal energy  ✔
42. The first law of thermodynamics is a restatement of the
   (1) law of conservation of momentum
   (2) Newton's law of cooling
   (3) law of conservation of mass
   (4) law of conservation of energy  ✔
43. A thermos flask contains hot tea. It is vigorously shaken. If the tea is considered as the system, then its temperature will
   (1) not change
   (2) rise ✔
   (3) fall
   (4) first fall and then rise
44. A mass of an ideal gas undergoes a reversible isothermal compression. Its molecules will then have compared with initial state, the same :
   (i) root mean square velocity
   (ii) mean momentum
   (iii) mean kinetic energy
   (1) If (i), (ii), (iii) correct ✔
   (2) If (i), (ii) correct
   (3) If (ii), (iii) correct
   (4) If (i) correct
45. A gas at NTP is suddenly compressed to one-fourth of its original volume. If y (gama) is supposed to be 3/2 ,then final pressure is
   (1) 4 atmosphere
   (2) 0.75 atmosphere
   (3) 8 atmosphere ✔
   (4) 0.25 atmosphere
46. A gas at NTP is slowly compressed to one-fourth of its original volume. Then final pressure is
   (1) 4 atmosphere ✔
   (2) 0.75 atmosphere
   (3) 8 atmosphere
   (4) 0.25 atmosphere
47. The work done in an adiabatic change in a particular gas depends upon only
   (1) change in specific heat
   (2) change in volume
   (3) change in pressure
   (4) change in temperature  ✔
48. In a cyclic process, the change in internal energy of a system over one complete cycle is
   (1) depends on the path
   (2) positive
   (3) negative
   (4) zero  ✔
49. A gas performs the most work when it expands
   (1) isothermally
   (2) adiabatically
   (3) at a non-uniform rate
   (4) isobarically ✔
50. Heating of water under atmospheric pressure is an
   (1) isothermal process
   (2) isobaric process ✔
   (3) adiabatic process
   (4) isochoric process
51. Boiling water is changing into steam. Under this condition, the specific heat of water is :
   (1) zero
   (2) one
   (3) infinite ✔
   (4) less than one
52. Which of following quantities must be determined to order that the thermal capacity of a body may be calculated, when the specific heat of body is known?
   (1) Emissivity
   (2) Latent heat
   (3) Mass ✔
   (4) Temperature
53. One mole of an ideal gas requires 207 J heat to raise the temperature by 10 K when heated at constant pressure. If the same gas heated at constant volume to raise the temperature by the same 10 K, then the heat required is :
   (1) 198.7 J
   (2) 215.3 J
   (3) 124 J ✔
   (4) 24 J
54. 70 calories of heat are required to raise the temperature of 2 moles of an ideal gas at constant pressure from 30° C to 35° C. The amount of heat required in calories to raise the temperature of same gas through the same range (30° C to 35° C)  at constant volume is :
   (1) 30
   (2) 50 ✔
   (3) 70
   (4) 90
55. When an ideal diatomic gas is heated at constant pressure, the fraction of the heat energy supplied which increases the internal energy of the gas is :
   (1) 2/5
   (2) 3/5
   (3) 3/7
   (4) 5/7 ✔
56. Temperature of argon kept in a vessel is raised by 1° C at constant volume. Heat supplied to the gas may be taken partly as (i) translational and partly (ii) rotational kinetic energies. Their respective shares are :
   (1) 60% , 40%
   (2) 50% , 50%
   (3) 100% , zero ✔
   (4) 40% , 60%
57. A mono-atomic ideal gas expands at constant pressure, with heat Q supplied. The fraction of Q which goes as work done by the gas is
   (1) 1
   (2) 2/3
   (3) 3/5
   (4) 2/5 ✔
58. For a gas y = 1.286. What is the number of degrees of freedom of the molecules of this gas?
   (1) 3
   (2) 5
   (3) 6
   (4) 7 ✔
59. 5 kg of water at 10° C is added to 10 kg of water at 40° C. Neglecting heat capacity of vessel and other losses, the equilibrium temperature will be close to :
   (1) 30° C  ✔
   (2) 25° C
   (3) 35° C
   (4) 33° C
60. 10 g of ice at – 20° C is added to 10 g of water at 50° C. The amount of ice in the mixture at resulting temperature is :
   (1) 10 g
   (2) 5 g ✔
   (3) 0 g
   (4) 20 g
61. 10 g of ice at – 20° C is added to 10 g of water at 50° C. Then the resulting temperature is :
   (1) – 20° C
   (2) 15° C
   (3) 0° C  ✔
   (4) 50° C
62. 10 g of ice cubes at 0° C is released in a tumbler containing water (water equivalent 55 g) at 40° C. Assuming that negligible heat is taken from surrounding, the temperature of water in the tumbler becomes nearly ( L = 80 cal/g)
   (1) 31° C
   (2) 22° C  ✔
   (3) 19° C
   (4) 15° C
63. A beaker contains 200 g of water. The heat capacity of beaker is equal to that of 20 g of water. The initial temperature of water in the beaker is 20° C. If 440 g of hot water at 92° C is poured in, the final temperature, neglecting radiation loss, will be nearest to :
   (1) 58° C
   (2) 68° C ✔
   (3) 73° C
   (4) 78° C
64. 80 g of water at 30° C is poured on a large block of ice at 0° C. The mass of ice that melts is :
   (1) 30 g  ✔
   (2) 80 g
   (3) 150 g
   (4) 1600 g
65. A gas has volume 3 litre when the thermometer reads 300 K. If the thermometer stands at 400 K, the volume of the gas will be close to
   (1) 4 litre
   (2) 9/4 litre
   (3) 1 litre
   (4) any value  ✔
66. A given quantity of an ideal gas is at pressure P and absolute temperature T. The isothermal bulk modulus of the gas is :
   (1) 2/3 P
   (2) P  ✔
   (3) 3/2 P
   (4) 2 P
67. Triple point of water is :
   (1) 373.16 K
   (2) 273.16 F
   (3) 273.16 K ✔
   (4) 273.16° C
68. The door of an operating refrigerator is opened. Now the temperature of the room will :
   (1) increase ✔
   (2) decrease
   (3) remain unchanged
   (4) decrease in summer and increase in winter
69. In the case of a petrol engine, the real useful work is done in the
   (1) exhaust stroke
   (2) suction stroke
   (3) compression stroke
   (4) explosion stroke  ✔
70. The function of the carburetor in a car engine is to :
   (1) filter the petrol before entering the piston chamber
   (2) form a proper mixture of air and petrol ✔
   (3) maintain a proper flow of petrol in the engine
   (4) check air from going into engine
71. A Carnot engine is working between 127° C and 27°C. The increase in efficiency will be maximum when the temperature of
   (1) the source is increased by 50° C
   (2) the sink is decreased by 50° C ✔
   (3) source is increased by 25° C and that of sink is decreased by 25° C
   (4) both source and sink are decreased by 25° C each
72. Ice contained in a beaker starts melting when
   (1) the specific heat of the system is zero
   (2) internal energy of the system remains constant
    (3) temperature remains constant ✔
    (4) entropy remains constant
73. During the melting of a slab of ice at 273 K at atmospheric pressure
    (1) positive work is done by ice-water system on the atmosphere
   (2) positive work is done on ice-water system by the atmosphere ✔
   (3) the internal energy of ice-water system increases ✔
   (4) the internal energy of ice-water system decreases
74. What is the coefficient of performance of a Carnot refrigerator working between 30° C and 0° C?
   (1) 0
   (2) 1
   (3) 9 ✔
   (4) 10
75. Metals are good conductors of heat because
   (1) they contain free electrons ✔
   (2) they are relatively far apart
   (3) their atoms collide very frequently
   (4) they have a reflecting surface
76. Heat is transmitted from higher to lower temperature through molecular collisions in
   (1) viscosity
   (2) radiation
   (3) convection
   (4) conduction  ✔
77. An ideal material for making cooking vessels must have
   (1) small conductivity and large heat capacity
   (2) large heat capacity and large conductivity
   (3) small heat capacity and large conductivity ✔
   (4) small heat capacity and small conductivity
78. Which of the following statements regarding thermal radiation is not correct  ?
   (1) A good absorber of thermal radiation is also a good emitter.
   (2) As the temperature of black-body emitter rises, the frequency at which the radiated energy is maximum decreases. ✔
   (3) The energy emitted by an opening in the wall of an enclosure is nearly identical with that which would be emitted by a black body at the same temperature as wall of an enclosure.
   (4) When a body is in equilibrium with its surrounding, the rate of thermal radiation is equal to the rate of absorption.
79. Ice starts forming in a lake with water at 0° C when the atmospheric temperature is – 10° C. If time taken for 1 cm of ice to be formed is 7 hours, the time taken for the thickness of ice to change from 1 cm to 2 cm is :
   (1) 3.5 hours
   (2) 7 hours
   (3) 14 hours
   (4) 21 hours  ✔
80. The intensity of radiation emitted by the Sun has its maximum value at a wavelength of 510 nm and that emitted by the North Star has the maximum value at 350 nm. If these stars behave like black bodies, then the ratio of the surface temperatures of the Sun and the North Star is :
   (1) 1.46
   (2) 0.69 ✔
   (3) 1.21
   (4) 0.83
81. An object is at temperature of 400° C. At what temperature would it radiate energy twice as first? The temperature of surroundings may be assumed to be negligible.
   (1) 200° C
   (2) 200 K
   (3) 800° C
   (4) 800 K  ✔
82. A wall has two layers A and B each made of different materials. Both layers have the same thickness. The thermal conductivity of the material of A is twice that of B. Under thermal equilibrium, the temperature difference across the wall is 36° C. The temperature difference across the layer A is :
   (1) 6° C
   (2) 12° C ✔
   (3) 18° C
   (4) 24° C
83. An unlagged cubic tank containing hot water loses heat to its surrounding at a rate of 900 W. This loss is reduced at 60 W, if all the faces of tank are covered with a layer of lagging. What will be the rate of loss of heat if one face is left unlagged? ( The temperature of the water and surroundings are unaltered. You may assume that heat is lost only from faces and that the rate of loss of heat from a face is unaffected by whether it is vertical or horizontal, top or bottom.)
   (1) 210 W
   (2) 200 W ✔
   (3) 190 W
   (4) 160 W
84. For an ideal gas, the heat capacity at constant pressure is larger than that at constant volume because work is done during expansion
   (1) of the gas by the external pressure
   (2) by the gas against external pressure ✔
   (3) by the gas against inermolecular forces of attraction
   (4) more collisions occur per unit time when volume is kept constant.
85. The energy emitted per second by a black body at 1227° C is E. Its temperature is raised to 4227° C. The energy emitted per second is :
   (1) 81 E ✔
   (2) 3 E
   (3) 9 E
   (4) 27 E
86. 1 g of steam at 100° C and an equal mass of ice at 0° C are mixed. The temperature of the mixture in steady state will be : ( Latent heat of steam = 540 cal/g and latent heat of ice = 80 cal/g )
   (1) 50° C
   (2) 100° C  ✔
   (3) 67° C
   (4) 33° C
87. A copper block A of mass 1 kg at 30° C and another copper block B of mass 0.1 kg at 100° C are kept in contact. Which of the following statements is / are true?
   (1) The steady state temperature of the system is 65° C.
   (2) The steady state temperature of the system is 30° C.
   (3) Heat flows from B to A.
   (4) Heat flows from A to B.  ✔
88. Water at 4° C has
   (1) maximum mass per unit volume. ✔
   (2) specific heat 1 cal/g/°C
   (3) minimum volume for unit mass ✔
   (4) maximum volume for unit mass
89. A body of mass 5 g is executing SHM about a point O with an amplitude of 10 cm. Its maximum velocity is 100 cm/s. Its velocity will be 50 cm/s at a distance (in cm)
   (1) 5
   (2) 5√2
   (3) 5√3 ✔
   (4) 10√2
90. A tunnel has been dug through the the diameter of the Earth and a ball is released in it. It executes a motion of time period :
   (1) 42 minute
   (2) 1 day
   (3) 1 hour
   (4) 84.6 minute  ✔
91. The displacement of particle executing SHM is given by y = 5 sin 20πt. Its frequency is
   (1) 10 Hz ✔
   (2) 20π Hz
   (3) 0.1 Hz
   (4) 20 Hz
92. The value of 'g' decreases by 0.1% on a mountain as compared to sea level. To record proper time here by means of simple pendulum, its length must be
   (1) increased by 0.1%
   (2) decreased by 0.1% ✔
   (3) increased by 0.2%
   (4) decreased by 0.2%
93. A particle executes SHM along a straight line so that its period is 12 s. The time it takes in traversing a distance equal to half its amplitude from its equilibrium position is
   (1) 6 s
   (2) 4 s
   (3) 2 s
   (4) 1 s ✔
94. A pendulum suspended from the ceiling of a train has a period T when the train is at rest. When the train is accelerating with a uniform acceleration, the period of oscillation will
   (1) increase
   (2) decrease ✔
   (3) remain unaffected
   (4) become infinite
95. A loaded spring vibrates with a period T. The spring is divided into nine equal parts and the same load is suspended from one of these parts. The new period is :
   (1) T
   (2) 3 T
   (3) T/3  ✔
   (4) T/9
96. A hollow metallic sphere is filled with water and hung by a long thread. A small hole is drilled at the bottom through which water slowly flows out. Now, the sphere is made to oscillate. The period of oscillation of sphere :
   (1) decreases
   (2) increases
   (3) remains constant
   (4) first increases and then decreases  ✔
97. The acceleration of a particle in simple harmonic motion is :
   (1) always zero
   (2) always constant
   (3) maximum at the extreme position ✔
   (4) maximum at the equilibrium position
98. If acceleration due to gravity is halved, then the frequency f of oscillation of a spring becomes :
   (1) 2 f
   (2) 4 f
   (3) f/2
   (4) No effect  ✔
99. The following are the quantities associated with a body performing SHM.
   1. The velocity of the body.
   2. The accelerating force acting on the body.
   3. The acceleration of the body.
Which of these quantities are exactly in phase with each other?
   (1) None of these
   (2) 1. and 2. only
   (3) 1. and 3. only
   (4) 2. and 3. only ✔
100. A 0.1 kg mass hanging from a light helical spring produces an equilibrium extension of 0.1 m. The mass is pulled vertically downwards by a distance of 0.02 m and then released. Taking g = 10 m/s², the equation relating displacement x of the mass from its equilibrium position and the time t after release is :
   (1) x = 0.1sin10t
   (2) x = 0.1cos0.2πt
   (3) x = 0.02sin0.2πt
   (4) x = 0.02cos10t  ✔

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