Friction Questions and Answers

A square wire frame ABCD lying in vertical plane is moving with a constant acceleration a into the plane as shown A bead can move along AC Coefficient of friction between wire and the bead is Choose the correct options EUR Grad ch en ado guich 1 as fachcut chi qua Agi A D A B a yg anfci a ABCD iz Aua azu a Ce f 52 Ahd 1 mz am fac C m A ta urucha g fl B Normal contact force on the bead is mg 2 m a Normal contact force on the bead is 4 2 At uruch da a 2 Correct Answer mg 2 Correct Answer The minimum acceleration a so that g bead does not slip is 2 gachi a fhuat fa yad ch 1 2 1 2 m D The minimum acceleration a so that bead does not slip is 1 ach a funt fay ya R ach

A class XII student presses her physics book against a roug vertical wall with her hand The direction of frictional force o the book exerted by the wall is Downwards Upwards Out from the wall Into the wall

In the figure a constant horizontal force is applied at the corner of a regular hexagon The hexagon starts to rotate in vertical plane and does not slide during the motion Initially the angular acceleration of the body is and magnitude of friction force is fo After the body had rotated through 5 degree the angular acceleration is r and magnitude of friction is f Then A a f fo B a f fo C a f fo D a a f fo

A ball of mass 1 kg and radius 10 cm is given an angular velocity 100 rad s and is then dropped from a height H 500 m from a point A above the ground The coefficient of restitution for the collision between the ball and the floor is 0 5 and coefficient of friction between the ball and the floor is 1 3 There is a smooth wall at a distance of 250 m from point O which is vertically below A The collision between the ball and wall is perfectly elastic Find the height at which the ball hits the wall Height of a ball expressed in power of 10 m is H 500 m A 0 B

Rod 1 of mass M 3kg and length L 2m is kept on a smooth horizontal surface Rod 2 AB of mass m 3kg and length Im is hinged at point A and just touches the Rod 2 as shown Find the minimum magnitude of force F required to move the Rod 1 1 20N F 2 15N u 0 5 Rod 2 3 10N a 450 Rod 1 4 5N

A uniform chain of mass m and length L rests on a rough table rd of its length hanging The table is tilted slowly and when inclination becomes 30 the chain just begins to slide Find coefficient of friction between the block and the table Ans 3 2

A bead constrained to move on rod in gravity free space as shown in figure The rod is rotating wi angular velocity and angular acceleration at about its end If is coefficient of friction Ma the correct option Rod rotates in the plane of paper A If u friction on bead is static in nature a B If friction on bead is kinetic in nature a C If u friction is static Bead

Q In which of the following cases the frictio nal force between the tyres of a car and the road increases 1 When the road is wet 2 When the speed of the car increases 3 When there are more passengers in the c ar 4 None of these

Two blocks of different masses are tied through a string and placed on a fixed wedge as shown in the figure The friction coefficient between the masses m and m2 with the incline is and respectively Find the condition for the string to remain tight throughout the motion An arrangement of pulley and masses are kept in an elevator which ascends with an acceleration of ao as shown in the figure Find the maximum force that can be applied on the block of mass m without disturbing the equilibrium of the system Em m m H fy A

38 A 40 kg slab rests on a frictionless floor as shown in the figure A 10 kg block rests on the top of the slab The static coefficient of friction between the block and the slab is 0 60 while the kinetic friction is 0 40 The 10 kg block is acted upon by a horizontal force 100N If g 9 8 m sec then resulting acceleration of the slab will be fa fa 40 kg 10 kg ich 0 60fch fach auch 0 40 ff g 9 8 m sec 1 0 90 m sec 100N 2 1 47 m sec 10 kg 40 kg 3 1 52 m sec 54 422 342 100 Net 4 6 1 m sec 10 kg

Particle A moves with speed 10 m s in a frictionless circular fixed horizontal pipe of radius 5 m and strikes with B of double mass that of A Coefficient of restitution is 1 2 and particle A starts its journey at t 0 The time at which second collision occurs is t 0 B R N T Fixed S 2T X QUE 1 6 Co MY F

6 2 10kg 20kg 1 a a 1 m s 1936 fo A A B a 3m s ag 0 pph A 3 3 a 3 m s a m s 2 4 a an m s 3 A overcrop 30

The max value of F for which both blocks move together is 0 5 is the coefficient of friction between two blocks LEXXYL 1 10 N 2 20 N 3 15 N 4 30 N 2 kg 4 kg Smooth surface 0 5 F www TOWr as 5X 6 x10 30

A block of mass 2 kg is pulled horizontally with the help of ideal string If a horizontal force of 5 N acts at the end of the string and block still stays at rest on a rough horizontal ground then the magnitude of frictional force acting on the block is N 20 N 1 Zero 2 kg 5 N manizantin mmm Rough horizontal ground V 2 2N N 9 A

A vehicle is moving on a road with an acceleration 40 m s as shown in figure The minimum coefficient of friction between the vehicle and the block so that the block does not fall downward is g 10 m s 1 0 10 2 0 25 3 0 05 4 0 20 a 40 m s AHO 1 Block 1x10x sin 80 x13

In each of the following cases find maximum horizontal force F upto which there is no relative slipping between the two blocks The horizontal surface is smooth and coefficient of friction between two blocks is u i F 2kg 3kg ii F 2kg 3kg

A block of mass 3kg is placed on a rough horizontal surface having coefficient of friction 0 10 between the block and horizontal surface Another block of mass 2 kg is placed on 3 kg block The coefficient of friction between two blocks is 0 20 Now the complete system is given velocity vo towards right then find the frictional force developed between two blocks and acceleration of each block 2kg 3kg Vo Vo

19 A well known experiment to demonstrate property of inertia is to pull out a cloth without letting a glass placed on it to fall The cloth spreads up to a length 1 from an edge of a table and the glass is placed on the cloth at a distance x x l from this edge Coefficient of friction between the cloth and the glass is u and that between the glass and the table is sufficient to prevent slipping of the glass on the table The glass can be considered as a point particle and the cloth light If the cloth is pulled with a constant speed find range of this speed for a successful demons tration of the experiment

Wedge is fixed on horizontal surface Triangular block A of mass M is pulled upward by applying a const force F parallel to incline of the wedge as shown in the figure and there is no friction between the wedge a the block A while coefficient of friction between A and block B of mass m is u If there is no relative mot between A and B then frictional force developed between A and B is F m M gsine 777 m cose M m B uma Wedge C F m M gsine m X m cose D mg 2

A block of mass M 6 kg is placed on an inclined plane raised 8 40 above the horizontal and attached to another block of mass m through a frictionless pulley If the coefficient of static friction between the block and the plane is p 0 2 what is the largest mass m the second block can have before it starts to fall m M

A system of three blocks of different masses is placed on a horizontal floor Blocks 2M and M are connected by a light string that passes over a frictionless pulley mounted on block 3M Block 2M is initially held in place Find the minimum value of the coefficient of static friction between block 3M and the floor that allows block 3M to remain at rest after block M is released The coefficients of friction between the block of mass 3M and that of mass 2M are given 14 0 40 14 0 35 s min 2M 3M M

pulling directly up the plane The sled is to be on the verge a sled is held on an inclined plane by a cord of moving up the plane In Fig 6 28b the magnitude F required of the cord s force on the sled is plotted versus a range of values for the coefficient of static friction between sled and plane F 2 0 N F 5 0 N and 0 25 At what angle is the plane inclined Ustrosinod joysti onnis ovib vales lo indicia F talooah in to geam di F 0 or lo 01 0 al F od tid d bes F 0 Figure 6 28 Problem 22 Se and sd moi vew a sid briw is i hill the ASE b H L

A chain of mass m and length is kept on a table as shown It is about to mov in this position If it is disturbed slightly then it falls off from table The total work done by friction is 0 32 mgl 0 mgl 16 0 mgl TH pooooo

Consider the following statements A Rolling friction can be smaller than static or sliding friction even by 2 or 3 times of magnitude B Lubricants are way of reducing static friction in a machine C Friction involved in ball bearings and surface in contact is rolling friction D A thin cushion of air maintained between solid surfaces in contact reduces friction The correct statements from above are A B C A B C A B C D A C D

A solid cylinder is kept at rest on a rough horizontal surface It is given a horizontal velocity Vo perpendicular to axis The time taken by it to start pure rolling is O l Vo 3 g 2V 3 g 3V 2 g Rough

A uniform disc of mass m and radius R is rolling down in an inclined plane which makes an angle of 60 degree with the horizontal If coefficient of friction is fl The magnitude of friction force acting on the disc is mg a The value of a is

7 20 A cylindrical vessel filled with water is released on a fixed inclined surface of angle as shown in figure 7 84 The friction coefficient of surface with vessel is u tan 0 Then the constant angle made by the surface of water with the incline will be Neglect the viscosity of liquid A tan l C 0 tan Fixed B 0 tan D cot Figure 7 84

6 A block of mass 2 kg is acted upon by a force F 200 N at 37 as shown The coefficient of static friction us between block and wall is 0 8 and coefficient of kinetic friction between block and wall is 0 5 The acceleration of block is 2kg

4 The figure shows a 15 kg solid cylinder mounted on a fixed axle with a radius 25 cm rotating at an angular speed of 500 rotations per minute If a 100 N braking force is applied normal to the curved surface of the cylinder bringing it to rest in 15 sec what is the coefficient of kinetic friction between the brake shoe and the cylinder approx Fixed axle a 0 027 C 0 066 b 0 042 d 0 140 Brake

Q 8 A force of 100 N is applied on a block of mass 3 kg as shown in figure The coefficient of friction between the surface and the block is 0 40 then the friction force acting on the block is a 90 N downwards b 12 N upwards 3 kg TTTTT

If block is in rest then friction on block oso masina Zo Esine Fixed mgs mgsin0 Fcose up along the inclined ng k 2 mgsin0 Fcose up along the inclined m 3 Fcose mgsine down along the inclined 0 Fros mgsin0 up along the inclined

1 A bar supporting a block on its top is placed on a frictionless plank that rests on a horizontal floor The bar is attached to a nail driven into the plank with the help of a spring as shown in the figure Coefficient of friction between the bar and the block is u What maximum acceleration parallel to the spring can the plank be given preventing sliding between A Mg the block and the bar Acceleration due to gravity is g 2 Towwwwww Alfem

A sphere is placed on a plank which is on smooth horizontal ground at rest An external constant force F is applied on the plank friction is sufficient to prevent slipping Choose the correc option s Acceleration of plank is more than sphere Kinetic friction is acting between plank and sphere rough smooth Kinetic energy of plank sphere system is equals to work done by external force F Work done by friction on sphere is positive

6 A block of mass m is put on a rough inclined plane of inclination 6 and is tied with a light thread shown Inclination is increased gradually from 0 0 to 9 90 Match the column according to corresponding curves Column I A Tension in the P thread versus 8 B Normal reaction Q between the block and the incline versus 8 C Friction force between the block and the incline versus 0 R D Net interaction 8 force between Column II

A cylinder is rotating about its axis and is in contact with a rough vertical wall and a rough horizontal surface Show the frictional force on the cylinder due to each surface Explain why is the normal force due to the ground less than the weight of the cylinder Discuss the situation if the direction of rotation of the cylinder is reversed

11 For the given situation shown in figure Choose the incorrect options g 10 ms 2 2kg 4kg H 0 4 Mk 0 2 Hg 0 6 M 0 4 A Att 1 s force of friction between 2 kg and 4 kg is 2 N B Att 1 s force of friction between 2 kg and 4 kg is zero C At t 4 s force of friction between 4 kg and ground is 8 N D Att 15 s acceleration of 2kg is 1 ms2 F 2t

is moving in forward direction with wheel rotating in clockwise direction What is the direction of of friction due to rough road and due to air acting on the car In forward direction by road and backward direction by air In forward direction by both road and air In backward direction by road and forward direction by air In backward direction by both road and air

A block of mass m 2 kg and another block of mass m 3kg are placed together see figure on an inclined plane with angle of inclination The coefficient of static and dynamic friction between the block m and the plane is always p 0 2 The coefficient of static and dynamic friction between the block m and the plane are equal to 0 3 13 Minimum angle at which both block start moving together is tan 1 50 m 0 Maximum angle up to which normal reaction between blocks remains 0 is tan 25

2 A block P of mass 5 kg is resting on the inclined surface of a wedge Q of mass 10 kg as shown The minimum value of coefficient of static friction between wedge and ground so that Q does not slip on ground should be A zero B 0 13 P 37 Q C 0 18 D 0 20 du

A zero B 0 13 Block A is placed on a rough wedge B which is placed on a smooth surface The wedge has angle of inclination of 53 and is imparted a horizontal acceleration g towards right Block A is given an initial velocity v with respect to wedge Find the coefficient of friction for which block A moves with constant velocity v with respect to wedge g 10 m s a g B 53 smooth surface 0 117 17

Blocks A and B have a mass of m and mB respectively and are connected to the massless links AC and BC shown below The coefficient of static friction between the blocks and the contacting surfaces is s The values of mA MB s and 0 are given on the Canvas page of your exam Use g 9 81 m s B C 0 P A

In the following figure a body of mass 1 2 kg is at rest at point P If R and F denote the reaction and the frictional force respectively then O O 30 P F R 6 N F 6 3 N R 3N F 3 3 N R 6N F 3N R 6 3 N F 6N

Two blocks A and B each of mass 2 kg connected by string are placed on rough horizontal surface Coefficient of friction between all the surface is 0 4 A force F 10 N act on block A B List I A Q Tension in string in N F P Friction force acting on block A in N 1 2 List II S Acceleration of blocks in m s 2 8 R Friction force acting on block B in N 3 0 4 3

Three blocks m m m are slid at constant velocity across a rough surface as shown The coefficient of kinetic friction between each block and the surface is u Find force applied by m on m A F m m gu m3 B m m gu 1 Mat m C m gu m m gu D m m m gu

The force required to just move a body up the inclined plane is double the force required to just prevent the body from sliding down the plane The coefficient of friction is u If 0 is the angle of inclination of the plane then tan 0 is equal to a b 3 c 2 d 0 5u

2 42 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 co efficient of static and kinetic friction are 0 5 0 4 respectively The acceleration of the body is Take g 10m s A 6 m s Im 25 m s2 B 1 m s

2 27 A block of mass 1 kg is horizontally thrown with a velocity of 10 m s on a stationary long plank of mass 2 kg whose surface has a 0 5 Plank rests on frictionless surface The time when m comes to rest w r t plank is A 2 sec 4 3 9 sec B 3 4 sec D 1 sec

2 48 A mass m rests under the action of a force F as shown in the figure 2 158 on a horizontal surface The coefficient a friction between the mass and the surface is u The force c friction between the mass and the surface is F A umg C F 3 130 Figure 2 158 F B mg 2 D mg F1

A block of mass 2 kg rests on a rough inclined plane making an angle 30 with the horizontal The coefficient of static friction between the block and the plane is 0 7 The frictional force on the block is 9 8 N 0 7 9 8 V N 9 8 7 N 0 8 9 8 N

A system consist of Blocks 5kg and Block 10kg lying on the table A force of 30 N is applied to the left as shown in Figure 2 a Calculate L The acceleration of the two blocks 3 marks The force of static friction between two Blocks Acceleration of 5 kg block must be the same as the combination 5kg 10 kg 30 N 3 marks