Unit 2 - Practice Quiz

1 Friction is a force that always acts in the direction ____ to the intended or actual motion.

2 Friction occurs due to the ____ of the surfaces in contact.

3 Which of the following is NOT a type of solid friction?

4 Friction experienced by a body when it slides over another body is known as:

5 The maximum value of static friction before motion begins is called:

6 If the applied force is less than the limiting friction, the body will:

7 The angle between the normal reaction and the resultant of normal reaction and limiting friction is called the:

8 The tangent of the angle of friction is equal to:

9 According to the laws of dry friction, the frictional force is directly proportional to the:

10 Does the coefficient of friction depend on the apparent area of contact?

11 Which of the following best describes the coefficient of friction?

12 Which friction is generally greater?

13 Dynamic friction is also known as:

14 The friction that exists when a body is at rest but on the verge of moving is:

15 When a block rests on a horizontal surface, the normal reaction is equal to:

16 If a body is moving on a rough horizontal surface with a constant velocity, the applied force is equal to:

17 The maximum angle of an inclined plane at which a body remains in equilibrium just by friction is called:

18 The angle of repose is always equal to the:

19 Friction is considered a 'necessary evil' because:

20 Which of the following generally has the lowest coefficient of friction?

21 A block of mass is placed on a rough inclined plane. If the angle of inclination is gradually increased, the block just begins to slide when . What is the coefficient of static friction between the block and the plane?

22 A block is at rest on a horizontal surface. The coefficient of static friction is $0.4$. If a horizontal force of is applied to the block, what is the magnitude of the frictional force acting on it? (Take )

23 A block is pressed against a vertical wall by a horizontal force . If the weight of the block is and the coefficient of static friction between the wall and the block is , what is the minimum value of required to prevent the block from falling?

24 According to the laws of dry friction (Coulomb friction), which of the following statements is true for a block sliding on a surface?

25 The angle of friction is defined as the angle between:

26 Why is it generally easier to pull a lawn mower at an angle to the horizontal than to push it at the same angle?

27 A body is sliding on a rough horizontal surface with an initial velocity . If the coefficient of kinetic friction is , the distance traveled by the body before coming to rest is:

28 A block weighing rests on a horizontal plane. A force of applied at an angle of upward from the horizontal just moves the block. What is the approximate coefficient of limiting friction?

29 Which of the following types of friction generally has the lowest magnitude for a given normal load?

30 At the microscopic level, what is the primary cause of dry friction between two solid metallic surfaces?

31 A block of mass slides down a rough incline of angle with constant velocity. What is the coefficient of kinetic friction ?

32 What is the 'cone of friction' in engineering mechanics?

33 A force is applied to a block to keep it moving at a constant speed across a rough surface. If the mass of the block is doubled while the nature of the surfaces remains the same, what new force is required to maintain constant speed?

34 Which of the following scenarios violates the standard laws of Coulomb (dry) friction?

35 A block of mass rests on a rough horizontal surface. A gradually increasing horizontal force is applied. The body will just start moving when reaches . The region where is characterized by:

36 A block of mass is pulled up a rough inclined plane of angle by a force parallel to the plane. If the block moves with acceleration and the coefficient of kinetic friction is , the equation of motion is:

37 Fluid friction (viscous drag) differs from solid dry friction in that fluid friction:

38 If the angle of repose for a given surface is , what is the coefficient of static friction?

39 A block rests on a horizontal floor. The coefficient of static friction is $0.3$ and kinetic friction is $0.2$. A horizontal force of is applied. What is the frictional force acting on the block?

40 When a solid cylindrical block is kept on a rough horizontal surface, and a horizontal force is applied at its center of mass, the direction of the frictional force exerted by the surface on the block is:

41 A block of weight rests on a rough inclined plane of inclination . If the angle of friction is and , the minimum horizontal force required to keep the block in equilibrium (preventing it from sliding down) is given by:

42 Two blocks and of weights and are connected by a string passing over a rough pulley with a coefficient of friction . If block is on the verge of moving downwards, the ratio of tensions is given by:

43 A body is sliding down an inclined plane with a constant velocity. If the plane is inclined at an angle to the horizontal, what can be deduced about the coefficients of static friction () and kinetic friction ()?

44 A solid cylinder of mass and radius is placed on a rough horizontal surface and pulled by a horizontal force applied at its top edge. What is the minimum coefficient of static friction required for pure rolling?

45 A block is placed on an inclined plane. The angle of the plane is gradually increased until the block just begins to slide. At this angle , a horizontal force is applied to push the block up the plane. The magnitude of required to initiate upward motion is:

46 A block of weight rests on a horizontal floor. A force is applied at an angle above the horizontal. To move the block with the minimum possible force , the angle should be:

47 A ladder of length and weight rests against a rough vertical wall and a rough horizontal floor. The coefficients of friction at the wall and floor are and respectively. If the ladder is on the verge of slipping, the angle it makes with the horizontal is given by:

48 Which of the following statements about rolling friction is fundamentally accurate in the context of deformable bodies?

49 According to Coulomb's laws of dry friction, how does the limiting friction depend on the macroscopic area of contact and the sliding velocity, assuming standard engineering approximations?

50 Two rough blocks and , of masses and , are stacked on a smooth horizontal table. A horizontal force is applied to block (the bottom block). The coefficient of static friction between the blocks is . What is the maximum force that can be applied such that block does not slide relative to ?

51 A wedge of angle is forced under a heavy block of weight resting on a horizontal floor. The coefficient of friction is for all surfaces, and the angle of friction is . The horizontal force required to drive the wedge is:

52 A block slides down a rough curved track. As it descends, its speed increases, but the normal force changes continuously. If the track is a quarter circle of radius and the block starts from rest at the top, the differential equation governing its speed as a function of the angle from the vertical incorporates kinetic friction. The normal force at any angle is:

53 A homogeneous cylinder rests on a V-block with angle . If the coefficient of static friction between the cylinder and the V-block is , the torque required to cause the cylinder to rotate in place is:

54 In the analysis of dry friction on a microscopic scale, the actual area of contact () is related to the apparent area of contact () and the normal load (). Which relationship best describes for metallic surfaces under plastic deformation asperities?

55 A block of mass is given an initial velocity up a rough inclined plane of angle . The coefficient of kinetic friction is . The ratio of the time taken to travel up the plane to the time taken to return to the starting point is:

56 A uniform rod of length and weight is supported by two pegs at distances and from the center of mass, on opposite sides. If the coefficient of friction is at both pegs, what is the maximum horizontal force applied at the center of mass along the rod before slipping occurs?

57 In Coulomb's theory, the frictional force vector during sliding is given by . If a block moves on a plane where a constant lateral force is applied perpendicular to its initial velocity, the path of the block becomes curved. The direction of the friction force:

58 For a block resting on a horizontal surface, a force is applied at an angle downwards from the horizontal. If is the angle of friction, the block cannot be made to slide, regardless of the magnitude of , if:

59 A uniform block of height and width rests on a rough inclined plane. The inclination of the plane is gradually increased. If the coefficient of static friction is , the block will topple before it slides if:

60 A belt passes over a fixed cylindrical drum of radius . The coefficient of friction is . If a tension is applied to one end, the minimum tension required at the other end to prevent slipping, given an angle of lap , is: