Tiêu đề 5.LAWS OF MOTION - Questions.pdf ✅

4.MOTION IN A PLANE (1.)The mass of man when standing on lift is 60 kg. What is the weight when he is standing on lift which is moving upwards with acceleration 4.9 ms−2 ? (a.) 882 kg (b.) 600 N (c.) 306 N (d.) Zero (2.)If a force of 250 N act on body, the momentum acquired is 125 kg-m/s. What is the period for which force acts on the body (a.) 0.5 sec (b.) 0.2 sec (c.) 0.4 sec (d.) 0.25 sec (3.)If μs , μk and μr are coefficients of static friction, sliding friction and rolling friction, then (a.) μs < μk < μr (b.) μk < μr < μs (c.) μr < μk < μs (d.) μr < μk < μs (4.)The mass of ship is 2 × 107 kg. On applying a force of 25 × 105 N , it is displaced through 25 m. After the displacement, the velocity acquired by the ship will be (a.) 12.5 m/s (b.) 5 m/s (c.) 3.7 m/s (d.) 2.5 m/s (5.)If rope of lift breaks suddenly, the tension exerted by the surface of lift (a = acceleration of lift) (a.) mg (b.) m(g + a) (c.) m(g − a) (d.) 0 (6.)A steel wire can withstand a load up to 2940 N. A load of 150 kg is suspended from a rigid support. The maximum angle through which the wire can be displaced from the mean position, so that the wire does not break when the load passes through the position of equilibrium, is (a.) 30° (b.) 60° (c.) 80° (d.) 85° (7.)A block P of mass m is placed on a frictionless horizontal surface. Another block Q of same mass is kept on Pand connected to the wall with the help of a spring of spring constant k as shown in the figure. μs is the coefficient of friction between P and Q. The blocks move together performing SHM of amplitude A. The maximum value of the friction force between P and Q is (a.) kA (b.) kA 2 (c.) Zero (d.) μsmg (8.)A light spring balance hangs from the hook of the other light spring balance and a block of mass M kg hangs from the former one. Then the true statement about the scale reading is (a.) Both the scales read M kg each (b.) The scale of the lower one reads M kg and of the upper one zero (c.) The reading of the two scales can be anything but the sum of reading will be M kg (d.) Both the scales read M/2 kg (9.)A shell of mass 10 kg is moving with a velocity of 10 ms−1 when it blasts and forms two parts of mass 9 kg and 1 kg respectively. If the 1st mass is stationary, the velocity of the 2nd is (a.) 1 ms−1 (b.) 10 ms−1 (c.) 100 ms−1 (d.) 1000 ms−1 (10.)Which of the following groups of forces could be in equilibrium (a.) 3 N, 4 N, 5N (b.) 4 N, 5 N, 10 N (c.) 30 N, 40 N, 80 N (d.) 1 N, 3 N, 5 N (11.)A lift is going up. The total mass of the lift and the passenger is 1500 kg the variation in the speed of the lift is as given in the graph. The tension in the rope pulling the lift at t = 11thsec will be (a.) 17400 N (b.) 14700 N (c.) 12000 N Smooth surface  P Q 3.6 speed in m/sec 2 10 12
(d.) Zero (12.)A lift of mass 1000 kg is moving with an acceleration of 1 m/s 2 in upward direction. Tension developed in the string, which is connected to the lift is (g = 9.8 m/s 2 ) (a.) 9,800 N (b.) 10,000 N (c.) 10, 800 N (d.) 11, 000 N (13.)The engine of a car produces an acceleration of 6 ms −2 in the car. If this car pulls another car of the same mass, then the acceleration would be (a.) 6 ms −2 (b.) 12 ms −2 (c.) 3 ms −2 (d.) 1.5 ms −2 (14.)Three blocks of masses m1, m2 and m3 are placed on a horizontal frictionless surface. A force of 40 N pulls the system then calculate the value of T, if m1 = 10 kg, m2 = 6 kg, m3 = 4 kg (a.) 40 N (b.) 20 N (c.) 10 N (d.) 5 N (15.)The pulley and strings shown in figure are smooth and of negligible mass. For the system to remain in equilibrium, the angle θ should be (a.) 0° (b.) 30° (c.) 45° (d.) 60° (16.)Two small balls of same size and masses m1 and m2 (m1 > m2) are tied by a thin weightless thread and dropped from a certain height. Training upward buoyancy force F into account, the tension T of the thread during the flight after the motion of the ball becomes uniform will be (a.) (m1 − m2)g (b.) (m1 − m2 )g/2 (c.) (m1 + m2 )g (d.) (m1 + m2 )g/2 (17.)A rocket of mass 1000 kg is exhaust gases at a rate of 4 kgs−1 with a velocity 3000 ms−1 . The thrust developed on the rocket is (a.) 12000 N (b.) 120 N (c.) 800 N (d.) 200 N (18.)A gardner waters the plants by a pipe of diameter 1mm. The water comes out at the rate or 10 cm3 /sec. The reactionary force exerted on the hand of the gardner is (a.) Zero (b.) 1.27 × 10−2 N (c.) 1.27 × 10−4 N (d.) 0.127 N (19.)The spring balance inside a lift suspends an object. As the lift begins to ascend, the reading indicated by the spring balance will (a.) Increase (b.) Decrease (c.) Remain unchanged (d.) Depend on the speed of ascend (20.)A body is moving along a rough horizontal surface with an initial velocity 6 m/s. If the body comes to rest after travelling 9m, then the coefficient of sliding friction will be (a.) 0.4 (b.) 0.2 (c.) 0.6 (d.) 0.8 (21.)A satellite in force-free space sweeps stationary interplanetary dust at a rate dM/dt = αv where M is the mass, v is the velocity of the satellite and α is a constant. What is the deacceleration of the satellite (a.) −2αv 2 /M (b.) −αv 2 /M (c.) +αv 2 /M (d.) −αv 2 (22.)A block of mass m is resting on a smooth horizontal surface. One end of a uniform rope of mass ( m 3 ) is fixed to the block, which is pulled in the horizontal direction by applying force F at the other end. The tension in the middle of the rope is (a.) 8 6 F (b.) 1 7 F (c.) 1 8 F (d.) 7 8 F (23.)Formula for true force is (a.) F = ma (b.) F = mdv dt (c.) F = dmv dt (d.) F = md 2x dt 2
(24.)A body of mass 8 kg is suspended through two light springs X and Y connected in series as shown in figure. The reading is X and Y respectively are (a.) 8 kg, zero (b.) Zero, 8 kg (c.) 6 kg, 2 kg (d.) 8 kg, 8 kg (25.)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 (26.)A packet of weight w is dropped with the help of a parachute and on striking the ground comes to rest with retardation equal to twice the acceleration due to gravity. What is the force exerted on the ground? (a.) w (b.) 2 w (c.) 3 w (d.) 4 w (27.)Newton’s first law of motion describes the following (a.) Energy (b.) Work (c.) Inertia (d.) Moment of inertia (28.)Two blocks A and B of masses 2m and m, respectively, are connected by a massless and inextensible string. The whole system is suspended by a massless spring as shown in the figure. The magnitudes of acceleration of A and B , immediately after the spring is cut, are respectively (a.) g, g/2 (b.) g/2, g (c.) g, g (d.) g/2, g/2 (29.)A body takes time t to reach the bottom of an inclined plane of angle θ with the horizontal. If the plane is made rough, time taken now is 2t. The coefficient of the friction of the rough surface is (a.) 3 4 tan θ (b.) 2 3 tan θ (c.) 1 4 tan θ (d.) 1 2 tan θ (30.)An object is subjected to a force in the north- east direction. To balance this force, a second force should be applied in the direction (a.) North-East (b.) South (c.) South-west (d.) West (31.)Maximum value of static friction is called (a.) Limiting friction (b.) Rolling friction (c.) Normal reaction (d.) Coefficient of friction (32.)A flat plate moves normally with a speed v1 towards a horizontal jet of water of uniform area of cross-section. The jet discharges water at the rate of volume V per second at a speed of v2. The density of water is ρ. Assume that water splashes along the surface of the plate at right angles to the original motion. The magnitude of the force acting on the plate due to the jet of water is (a.) ρVv1 (b.) ρV(v1 + v2) (c.) ρV v1+v2 v1 2 (d.) ρ [ V v2 ] (v1 + v2 ) 2 (33.)When a body is stationary (a.) There is no force acting on it (b.) The force acting on it is not in contact with it (c.) The combination of forces acting on it balances each other (d.) The body is in vacuum (34.)A passenger is travelling in a train moving at 72 kmh −1 . His suitcase is kept on the berth. The driver of the train applies brakes such that the speed of the train decreases at a constant rate of 36 kmh −1 in 5 s. What should be the minimum coefficient of friction between the suitcase and the berth if the suitcase is not the slide during retardation of the train? (a.) 10 49 (b.) 10 98 (c.) 28 49
(d.) 30 98 (35.)The minimum force required to start pushing a body up a rough (frictional coefficient μ) inclined plane is F1 while the minimum force needed to prevent it from sliding down is F2. If the inclined plane makes an angle θ from the horizontal such that tan θ = 2μ, then the ratio F1 F2 is (a.) 4 (b.) 1 (c.) 2 (d.) 3 (36.)A horizontal force of 10 N is necessary to just hold a block stationary against a wall. The coefficient of friction between the block and the wall is 0.2. The weight of the block is (a.) 2 N (b.) 20 N (c.) 50 N (d.) 100 N (37.)A stick of 1 m is moving with velocity of 2.7 × 108 ms −1 . What is the apparent length of the stick (c = 3 × 108 ms −1 ) (a.) 10 m (b.) 0.22 m (c.) 0.44 m (d.) 2.4 m (38.)A ball of mass 0.2 kg rests on a vertical post of height 5 m. A bullet of mass 0.01 kg, travelling with a velocity v m/s in a horizontal direction, hits the centre of the ball. After the collision, the ball and bullet travel independently. The ball hits the ground at a distance of 20 m and the bullet at ball hits the ground at a distance of 100 m from the foot of the post. The initial velocity v of the bullet is (a.) 250 m/s (b.) 250√2 m/s (c.) 400 m/s (d.) 500 m/s (39.)A smooth block is released at rest on a 45° incline and then slides a distance d. The time taken to slide is n times as much to slide on rough incline than on a smooth incline. The coefficient of friction is (a.) μk = 1 − 1 n2 (b.) μk = √1 − 1 n2 (c.) μs = 1 − 1 n2 (d.) μs = √1 − 1 n2 (40.)A man fires a bullet of mass 200 g at a speed of 5 m/s . The gun is of one kg mass. By what velocity the gun rebounds backwards (a.) 0.1 m/s (b.) 10 m/s (c.) 1 m/s (d.) 0.01 m/s (41.)A block of mass m is pushed with a velocity u towards a movable wedge of mass nm and height h, figure. All the surfaces are smooth. The minimum value of u for which the block will reach the top of wedge is (a.) √2gh (1 − 1 n ) (b.) √2gh (1 + 1 n ) (c.) √3gh (d.) √2gh (42.)The engine of a jet aircraft applies a thrust force of 105N during take off and causes the plane to attain a velocity of 1 km/sec in 10 sec. The mass of the plane is (a.) 102 kg (b.) 103 kg (c.) 104kg (d.) 105kg (43.)Three concurrent co-planar forces 1 N, 2 N and 3 N acting along different directions on a body (a.) Can keep the body in equilibrium if 2 N and 3 N act at right angle (b.) Can keep the body in equilibrium if 1 N and 2 N act at right angle (c.) Cannot keep the body in equilibrium (d.) Can keep the body in equilibrium if 1 N and 3 N act at an acute angle (44.)Sand is being dropped on a conveyor belt at the rate of M kg/s. The force necessary to keep the belt moving with a constant velocity of v m/s will be (a.) Mv 2 newton (b.) Zero (c.) Mv newton (d.) 2 Mv newton (45.)A uniform rope of length l lies on a table. If the coefficient of friction is μ, then the maximum length l1 of the part of this rope which can overhang from the edge of the table without sliding down is 10 N