Tiêu đề Friction (A & R) E.pdf ✅

PHYSICS The following question given below consist of an "Assertion" (A) and "Reason" (R) Type questions. Use the following Key to choose the appropriate answer. (A) If both (A) and (R) are true, and (R) is the correct explanation of (A). (B) If both (A) and (R) are true but (R) is not the correct explanation of (A). (C) If (A) is true but (R) is false. (D) If (A) is false but (R) is true. Q. 1 Assertion : Due to frictional force acting on a body, the body is always retarded by friction. Reason : Friction force opposes the slipping between the surfaces in contact. [D] Q. 2 Assertion : Work done by static friction is always zero. Reason : Static friction between two surface in contact acts when they are not slipping over each other but there is a tendency of slipping between them. [D] Q.3 Assertion : Work done by frictional force may be sometimes path independent. Reason : Frictional force is a non-conservative force. [B] Q. 4 Assertion : Work done by frictional force can not be positive. Reason : Work done is positive when force acts in the direction of displacement. Sol. [D] Work done by static friction may be positive. Q. 5 Assertion : Due to frictional force acting on a body, the body is always retarded by friction. Reason : Friction force opposes the slipping between the surfaces in contact. [D] Q.6 Assertion : Work done by static friction acting on body is always zero. Reason : Static friction on a body kept on a surfaces acts when the body is not slipping on it but there is a tandency of slipping. [D] Q.7 Assertion : When a body is at rest on a horizontal surface then the contact force on the body by the surface must be equal to the weight of body. Reason : The contact force is the total force applied by the surface on the body kept on it. Sol. [D] Static friction may act even when body remain at rest Q.8 Assertion/Statement : Pulling a lawn roller is easier than pushing it. Reason/Statement : Pushing increases the apparent weight and hence the force of friction. [A] Q.9 Assertion/Statement : Static friction is a self adjusting force. Reason/Statement : The magnitude of static friction is equal to the applied force and its direction is opposite to that of the applied force. [C] Q.10 Assertion/Statement : A horse has to pull a cart harder during the first few steps of his motion. Reason/Statement : The first few steps are always difficult. [C] Q.11 Assertion/Statement : Force of friction increases when surfaces in contact are too smooth. Reason/Statement : Smoothness decreases friction. [C]
Q.12 Assertion/Statement : A block of mass m starts moving on a rough horizontal surface with a velocity v. It stops due to friction between the block and the surface after moving through a certain distance. The surface is now tilted to an angle of 30o with the horizontal and the same block is made to go up on the surface with the same initial velocity v. The decrease in the mechanical energy in the second situation is smaller than that in the first situation. Reason/Statement : The coefficient of friction between the block and the surface decreases with the increase in the angle of inclination. [IIT - 2007] [C] Q.13 Assertion/Statement : It is easier to pull a heavy object than to push it on a level ground. Reason/Statement : The magnitude of frictional force depends on the nature of the two surfaces in contact. [IIT-2008] [B] Q.14 Assertion : Static friction acts between two surfaces in contact only when these surfaces are at rest with respect to ground. Reason : Static friction opposes the slipping between surfaces. [D] Q.15 Statement I : Pulling a lawn roller is easier than pushing it. Statement II : Pushing increases the apparent weight and hence force of friction. [A] Q.16 Statement I : The force of friction in the case of a disc rolling without slipping down an inclined plane is zero. Statement II : When the disc rolls without slipping, friction is required because for rolling condition velocity of point of contact is zero. [D] Q.17 Statement I : Friction is self adjusting force. Statement II : The magnitude of static friction is equal to the applied force and its direction is opposite to that of the applied force. [D] Q.18 Assertion : A coin is placed on phonogram turn table. The motor is started, coin moves along the moving table. Reason : Rotating table is providing necessary centripetal force to the coin. (A) a (B) b (C) c (D) d [A] Q.19 Assertion : By pressing a block against a rough wall, one can balance it. Reason : Smooth walls can not hold the block by pressing the block against the wall, however high the force is exerted. (A) a (B) b (C) c (D) d [B] Q.20 Assertion : The value of dynamic friction is less than the limiting friction. Reason : Once the motion has started, the inertia of rest has been overcome. (A) a (B) b (C) c (D) d [A] Q.21 Assertion : The acceleration of a body down a rough inclined plane is greater than the acceleration due to gravity. Reason : The body is able to slide on a inclined plane only when its acceleration is greater than acceleration due to gravity (A) a (B) b (C) c (D) d [D] Q.22 STATEMENT - 1 A block of mass m starts moving on a rough horizontal surface with a velocity v. It stops due to friction between the block and the surface after moving through a certain distance. The surface is now tilted to an angle of 30o with the horizontal and the same block is made to go up on the surface with the same initial velocity v. The decrease in the mechanical energy in the second situation is smaller than that in the first situation. [IIT - 2007] Because STATEMENT - 2 The coefficient of friction between the block and the surface decreases with the increase in the angle of inclination. [B] Q.23 STATEMENT –1
A cloth covers a table. Some dishes are kept on it. The cloth can be pulled out without dislodging the dishes from the table. because STATEMENT –2 For every action there is an equal and opposite reaction. [IIT - 2007] [B] Q.24 STATEMENT - 1 [IIT-2008] It is easier to pull a heavy object than to push it on a level ground. and STATEMENT - 2 The magnitude of frictional force depends on the nature of the two surfaces in contact. [B] Q.25 Assertion : When a man climbs the rope friction force acts in downward direction. Reason : Friction force opposes relative motion or tendency of relative motion between two contact surfaces. [D] Sol. mg f When man climbs the rope, there is tendency to slip down the rope because of his weight & hence friction acts upward. Q.26 Assertion : Kinetic friction on a moving body always acts opposite to the net external force acting on the body. Reason : Friction always opposes the relative motion between the surfaces in contact. [D] Sol. Kinetic friction opposes slipping. Q.27 Assertion : A body is lying at rest on a rough horizontal surface. A person accelerating with acceleration (a i ˆ ), where i ˆ is in horizontal direction, observes the body, with respect to him, the block experiences a kinetic friction. Reason : Whenever there is relative motion between the contact surfaces then kinetic friction acts. [D] Q.28 Statement-1 : Work-done by frictional force is always negative. Statement-2 : Frictional force always opposes the relative motion at contact surface. [D] Sol. In case of walking work-done by frictional force in not negative. Q.29 Assertion (A) : Work done by static friction acting on body is always zero. Reason (R) : Static friction on a body kept on a surfaces acts when the body is not slipping on it but there is a tendency of slipping. [D] Sol. Conceptual Q.30 Assertion : The work done by friction force on a body is always negative. Reason : Friction force is non conservative force. Sol.[D] (A) is false but (R) is true Q. 31 Assertion : Due to frictional force acting on a body, the body is always retarded by friction. Reason : Friction force opposes the slipping between the surfaces in contact. Sol.[D] Q.32 Assertion : Work done by static friction is always zero. Reason : Static friction between two surface in contact acts when they are not slipping over each other but there is a tendency of slipping between them. Sol.[D] Work done by static friction may not be zero.