Tiêu đề 06. FRICTION EASY.pdf ✅

1. The coefficient of friction  and the angle of friction  are related as (a) sin  =  (b) cos  =  (c) tan  =  (d) tan  =  2. A force of 98 N is required to just start moving a body of mass 100 kg over ice. The coefficient of static friction is (a) 0.6 (b) 0.4 (c) 0.2 (d) 0.1 3. A block weighs W is held against a vertical wall by applying a horizontal force F. The minimum value of F needed to hold the block is (a) Less than W (b) Equal to W (c) Greater than W (d) Data is insufficient 4. The maximum static frictional force is (a) Equal to twice the area of surface in contact (b) Independent of the area of surface in contact (c) Equal to the area of surface in contact (d) None of the above 5. Pulling force making an angle  to the horizontal is applied on a block of weight W placed on a horizontal table. If the angle of friction is  , then the magnitude of force required to move the body is equal to (a) tan( ) sin    g − W (b) cos( ) cos    − W (c) cos( ) sin    − W (d) sin( ) tan    − W 6. In the figure shown, a block of weight 10 N resting on a horizontal surface. The coefficient of static friction between the block and the surface s = 0.4 . A force of 3.5 N will keep the block in uniform motion, once it has been set in motion. A horizontal force of 3 N is applied to the block, then the block will (a) Move over the surface with constant velocity (b) Move having accelerated motion over the surface (c) Not move (d) First it will move with a constant velocity for some time and then will have accelerated motion 7. Two masses A and B of 10 kg and 5 kg respectively are connected with a string passing over a frictionless pulley fixed at the corner of a table as shown. The coefficient of static friction of A with table is 0.2. The minimum mass of C that may be placed on A to prevent it from moving is (a) 15 kg (b) 10 kg (c) 5 kg (d) 12 kg 8. The limiting friction is (a) Always greater than the dynamic friction (b) Always less than the dynamic friction (c) Equal to the dynamic friction (d) Sometimes greater and sometimes less than the dynamic friction 9. Which is a suitable method to decrease friction (a) Ball and bearings (b) Lubrication (c) Polishing (d) All the above 10. A uniform rope of length l lies on a table. If the coefficient of friction is  , then the maximum length 1 l of the part of this rope which can overhang from the edge of the table without sliding down is (a)  l (b) l l  + (c)   1 + l (d)  −1 l 11. Which of the following statements is not true (a) The coefficient of friction between two surfaces increases as the surface in contact are made rough (b) The force of friction acts in a direction opposite to the applied force (c) Rolling friction is greater than sliding friction (d) The coefficient of friction between wood and wood is less than 1 12. A block of 1 kg is stopped against a wall by applying a force F perpendicular to the wall. If  = 0.2 then minimum value of F will be (a) 980 N (b) 49 N (c) 98 N (d) 490 N T A C B
13. A heavy uniform chain lies on a horizontal table-top. If the coefficient of friction between the chain and table surface is 0.25, then the maximum fraction of length of the chain, that can hang over one edge of the table is (a) 20% (b) 25% (c) 35% (d) 15% 14. The blocks A and B are arranged as shown in the figure. The pulley is frictionless. The mass of A is 10 kg. The coefficient of friction of A with the horizontal surface is 0.20. The minimum mass of B to start the motion will be (a) 2 kg (b) 0.2 kg (c) 5 kg (d) 10 kg 15. Work done by a frictional force is (a) Negative (b) Positive (c) Zero (d) All of the above 16. A uniform chain of length L changes partly from a table which is kept in equilibrium by friction. The maximum length that can withstand without slipping is l, then coefficient of friction between the table and the chain is (a) L l (b) L l l + (c) L l l − (d) L l L + 17. When two surfaces are coated with a lubricant, then they (a) Stick to each other (b) Slide upon each other (c) Roll upon each other (d) None of these. 18. A 20 kg block is initially at rest on a rough horizontal surface. A horizontal force of 75 N is required to set the block in motion. After it is in motion, a horizontal force of 60 N is required to keep the block moving with constant speed. The coefficient of static friction is (a) 0.38 (b) 0.44 (c) 0.52 (d) 0.60 19. A block A with mass 100 kg is resting on another block B of mass 200 kg. As shown in figure a horizontal rope tied to a wall holds it. The coefficient of friction between A and B is 0.2 while coefficient of friction between B and the ground is 0.3. The minimum required force F to start moving B will be (a) 900 N (b) 100 N (c) 1100 N (d) 1200 N 20. To avoid slipping while walking on ice, one should take smaller steps because of the (a) Friction of ice is large (b) Larger normal reaction (c) Friction of ice is small (d) Smaller normal reaction 21. A box is lying on an inclined plane what is the coefficient of static friction if the box starts sliding when an angle of inclination is 60o (a) 1.173 (b) 1.732 (c) 2.732 (d) 1.677 22. A block of mass 2 kg is kept on the floor. The coefficient of static friction is 0.4. If a force F of 2.5 Newtons is applied on the block as shown in the figure, the frictional force between the block and the floor will be (a) 2.5 N (b) 5 N (c) 7.84 N (d) 10 N 23. Which one of the following is not used to reduce friction (a) Oil (b) Ball bearings (c) Sand (d) Graphite 24. If a ladder weighing 250N is placed against a smooth vertical wall having coefficient of friction between it and floor is 0.3, then what is the maximum force of friction available at the point of contact between the ladder and the floor (a) 75 N (b) 50 N (c) 35 N (d) 25 N 25. A body of mass 2 kg is kept by pressing to a vertical wall by a force of 100 N. The coefficient of friction between wall and body is 0.3. Then the frictional force is equal to (a) 6 N (b) 20 N (c) 600 N (d) 700 N 26. 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 A B B A F F 10 N
27. The coefficient of static friction, ,  s between block A of mass 2 kg and the table as shown in the figure is 0.2. What would be the maximum mass value of block B so that the two blocks do not move? The string and the pulley are assumed to be smooth and massless. ( 10 / ) 2 g = m s (a) 2.0 kg (b) 4.0 kg (c) 0.2 kg (d) 0.4 kg 28. If mass of A = 10 kg , coefficient of static friction = 0.2, coefficient of kinetic friction = 0.2. Then mass of B to start motion is (a) 2 kg (b) 2.2 kg (c) 4.8 kg (d) 200 gm 29. A uniform metal chain is placed on a rough table such that one end of chain hangs down over the edge of the table. When one- third of its length hangs over the edge, the chain starts sliding. Then, the coefficient of static friction is (a) 4 3 (b) 4 1 (c) 3 2 (d) 2 1 30. A lift is moving downwards with an acceleration equal to acceleration due to gravity. A body of mass m kept on the floor of the lift is pulled horizontally. If the coefficient of friction is , then the frictional resistance offered by the body is (a) mg (b) mg (c) 2mg (d) Zero 31. If a ladder weighing 250 N is placed against a smooth vertical wall having coefficient of friction between it and floor is 0.3, then what is the maximum force of friction available at the point of contact between the ladder and the floor (a) 75 N (b) 50 N (c) 35 N (d) 25 N 32. Which one of the following statements is correct (a) Rolling friction is greater than sliding friction (b) Rolling friction is less than sliding friction (c) Rolling friction is equal to sliding friction (d) Rolling friction and sliding friction are same 33. The maximum speed that can be achieved without skidding by a car on a circular unbanked road of radius R and coefficient of static friction  , is (a) Rg (b) Rg  (c)  Rg (d) Rg 34. A car is moving along a straight horizontal road with a speed 0 v . If the coefficient of friction between the tyres and the road is  , the shortest distance in which the car can be stopped is (a) g v 2 2 0 (b) g v  0 (c) 2 0         g v  (d)  0 v 35. A block of mass 5 kg is on a rough horizontal surface and is at rest. Now a force of 24 N is imparted to it with negligible impulse. If the coefficient of kinetic friction is 0.4 and 2 g = 9.8 m / s , then the acceleration of the block is (a) 2 0.26 m / s (b) 2 0.39 m / s (c) 2 0.69 m / s (d) 2 0.88 m / s 36. A body of mass 2 kg is being dragged with uniform velocity of 2 m/s on a rough horizontal plane. The coefficient of friction between the body and the surface is 0.20. The amount of heat generated in 5 sec is (J = 4.2 joule / cal and 9.8 / ) 2 g = m s (a) 9.33 cal (b) 10.21 cal (c) 12.67 cal (d) 13.34 cal 37. Two carts of masses 200 kg and 300 kg on horizontal rails are pushed apart. Suppose the coefficient of friction between the carts and the rails are same. If the 200 kg cart travels a distance of 36 m and stops, then the distance travelled by the cart weighing 300 kg is (a) 32 m (b) 24 m (c) 16 m (d) 12 m 38. A body B lies on a smooth horizontal table and another body A is placed on B. The coefficient of friction between A and B is  . What acceleration given to B will cause slipping to occur between A and B (a) g (b) g /  (c)  / g (d) g A B 2 kg A B 10 kg A B
39. A 60 kg body is pushed with just enough force to start it moving across a floor and the same force continues to act afterwards. The coefficient of static friction and sliding friction are 0.5 and 0.4 respectively. The acceleration of the body is (a) 2 6 m / s (b) 2 4.9 m / s (c) 2 3.92 m / s (d) 2 1m / s 40. A car turns a corner on a slippery road at a constant speed of 10 m / s . If the coefficient of friction is 0.5, the minimum radius of the arc in meter in which the car turns is (a) 20 (b) 10 (c) 5 (d) 4 41. A motorcyclist of mass m is to negotiate a curve of radius r with a speed v. The minimum value of the coefficient of friction so that this negotiation may take place safely, is (a) v rg 2 (b) gr v 2 (c) 2 v gr (d) v r g 2 42. On a rough horizontal surface, a body of mass 2 kg is given a velocity of 10 m/s. If the coefficient of friction is 0.2 and 2 g = 10 m / s , the body will stop after covering a distance of (a) 10 m (b) 25 m (c) 50 m (d) 250 m 43. A block of mass 50 kg can slide on a rough horizontal surface. The coefficient of friction between the block and the surface is 0.6. The least force of pull acting at an angle of 30° to the upward drawn vertical which causes the block to just slide is (a) 29.43 N (b) 219.6 N (c) 21.96 N (d) 294.3 N 44. A body of 10 kg is acted by a force of 129.4 N if 2 g = 9.8 m / sec . The acceleration of the block is 2 10 m / s . What is the coefficient of kinetic friction (a) 0.03 (b) 0.01 (c) 0.30 (d) 0.25 45. Assuming the coefficient of friction between the road and tyres of a car to be 0.5, the maximum speed with which the car can move round a curve of 40.0 m radius without slipping, if the road is unbanked, should be (a) 25 m/s (b) 19 m/s (c) 14 m/s (d) 11 m/s 46. Consider a car moving along a straight horizontal road with a speed of 72 km/h. If the coefficient of kinetic friction between the tyres and the road is 0.5, the shortest distance in which the car can be stopped is [ 10 ] −2 g = ms (a) 30 m (b) 40 m (c) 72 m (d) 20 m 47. A 500 kg horse pulls a cart of mass 1500 kg along a level road with an acceleration of 2 1 − ms . If the coefficient of sliding friction is 0.2, then the force exerted by the horse in forward direction is (a) 3000 N (b) 4000 N (c) 5000 N (d) 6000 N 48. The maximum speed of a car on a road turn of radius 30m; if the coefficient of friction between the tyres and the road is 0.4; will be (a) 9.84 m/s (b) 10.84 m/s (c) 7.84 m/s (d) 5.84 m/s 49. A block of mass 50 kg slides over a horizontal distance of 1 m. If the coefficient of friction between their surfaces is 0.2, then work done against friction is (a) 98 J (b) 72J (c) 56 J (d) 34 J 50. On the horizontal surface of a truck ( = 0.6), a block of mass 1 kg is placed. If the truck is accelerating at the rate of 5m/sec2 then frictional force on the block will be (a) 5 N (b) 6 N (c) 5.88 N (d) 8 N 51. A vehicle of mass m is moving on a rough horizontal road with momentum P. If the coefficient of friction between the tyres and the road be , then the stopping distance is (a) m g P 2 (b) m g P 2 2 (c) m g P 2 2 (d) m g P 2 2 2 52. A body of weight 64 N is pushed with just enough force to start it moving across a horizontal floor and the same force continues to act afterwards. If the coefficients of static and dynamic friction are 0.6 and 0.4 respectively, the acceleration of the body will be (Acceleration due to gravity = g) (a) 6.4 g (b) 0.64 g (c) 32 g (d) 0.2 g 53. When a body is moving on a surface, the force of friction is called (a) Static friction (b) Dynamic friction (c) Limiting friction (d) Rolling friction 54. A block of mass 10 kg is placed on a rough horizontal surface having coefficient of friction  = 0.5. If a horizontal force of