Friction Questions and Answers

1 0 1 N 3 0 5 N 2 2N 4 5 N 7 The tension T in the string shown in figure is 1 Zero 10kg 30 0 7 2 50 N

1 Prevents the relative motion between them 2 Opposite to the direction of motion of them 3 Acts in opposite direction of applied force 4 Both 1 2 5 Coefficient of kinetic friction and coefficient of static friction between two blocks is and respectivley In general 2 1 4 None of these The limiting value of static friction between two contact surfaces is 1 3 P P

A hemisphere of radius R 0 5 m is rotated with a uniform angular speed 10 rad sec for some time The hemisphere is then stopped and it was found that only 20 of its top surface area remained covered with dust particles Find the coefficient of friction between the particles and the hemisphere dus

A bead of mass m slide down with constant speed on a helical wire as shown where h is the vertical displacement of the particle one complete revolution then magnitude of work done by friction in one complete revolution O mgh O will depend on speed of the particle O less then mgh more than mgh m Save

Consider a block of mass m 10 kg kept on a smooth horizontal table as shown in the figure If a horizontal force of 5 N acts on the block the value of frictional force exerted by the table on the block will be 10 kg 5 N 7 05N O 10 N 02N O Zero

Figure shows two blocks of mass m M connected with a string on a vertical wall m is pushed against the wall with a force F and no block moves If u is the coefficient of friction between wall and blocks then A Friction on mis mg B Friction on M is 0 C Friction on m is F M F D Force F should be greater or equal to M m 2

1 The velocity time graph of the fig shows the motion of a wooden block of mass 1 kg which is given an initial push at t 0 along a horizontal table g 10ms V ms 4 0 0 t sec A The coefficient of friction between the block and the table is 0 1 B The coefficient of friction between the block and the table is 0 2 C If the table has half of its present roughness the time taken by the block to complete the journey is 4 sec D If the table has half of its present roughness the time taken by the block to complete the journey is 8 sec

PAB 0 5 PBC 0 5 PGD 0 5 PD ground Consider a four block system Two forces act on the system as shown in figure F 100 N C B A 10 kg 10 kg 10 kg 10 kg F 20 N Smooth ground Choose the correct statement s A The acceleration of block D is 2 m s B The force of friction between C and D is 20 N C The force of friction between B and C is 60 N D The acceleration of C is 2 m s

Consider a four block system Two forces act on the system as shown in figure Here UAB 0 5 HBC 0 5 HcD 0 5 HD ground 0 Choose the correct statement s The acceleration of block D is 2 m s The force of friction between C and D is 20 N The force of friction between B and C is 60 N 100 N C D F B A 10 kg 10 kg 10 kg 10 kg F 20 N Smooth ground

In Figure the co efficient of friction between the floor and the body B is 0 1 The co efficient of friction between the bodies B and A is 0 2 A force F is applied as shown on B The mass of A is m 2 and of B is m Which of the following statements are true B A 1 The bodies will move together if F 0 25 mg 2 The body A will slip with respect to B if F 0 5 mg 3 The maximum value of F for which the two bodies will move together is 0 45 mg 4 All of these

HAB 0 5 HBC 0 5 HCD 0 5 HD ground Consider a four block system Two forces act on the system as shown in figure Choose the correct statement s The acceleration of block D is 2 m s 0 The force of friction between C and D is 20 N The acceleration of C is 2 m s The force of friction between B and C is 60 N F2 100 N D A B 10 kg 10 kg 10 kg 10 kg F 20 N Smooth ground

5 A 7 96 kg block rests on a plane inclined at 22 0 to the hori zontal as shown in Fig 5 48 The coefficient of static friction is 0 25 while the coefficient of kinetic friction is 0 15 a What is the minimum force F parallel to the plane that will prevent the block from slipping down the plane b What is the minimum force F that will start the block moving up the plane c What force F is required to move the block up the plane at constant velocity 22 0

Two persons manage to push a motorcar of mass 600 kg at a uniform velocity along a level road The same motorcar can be pushed by three persons to produce an acceleration of 0 2 ms 2 with what force does each person push the motorcar A 200 N C 140 N B 150 N D 120 N

Find the minimum coefficient of friction 0 between the 1 kg block and the surface so that the system of three masses does move on the surface under the action of 20 N force Take g 10 ms 1kg 10kg H 0 3 O 0 2 O 0 5 208 0 1 2kg 0 1 20N

T he acceleration of free fall is g current at which 25 A thin uniform conducting disc of radius r and mass m rests on a horizontal tabletop where a uniform magnetic field of induction B pointing vertically upwards exists Coefficient of friction between the disc and the tabletop is u Two points P and P2 on the rim of the disc are connected with two flexible wires which facilitate a current to flow through the disc The contact points P and P2 subtend an angle at the centre of the disc How much minimum current must flow through the disc so that it begins to slide Acceleration of free fall is g A conducting fluid of maca dons poristivity fe is kept O B I O P O O O O O O Pz 1 O O 7 O O O

Zero Marks 0 In all other cases A block of mass 2 kg is pushed normally against a rough vertically wall with a force of 40 N coefficient of static friction being 0 5 Another horizontal force of 15 N is applied on the block in a direction parallel to the wa Acceleration in m s of the block is

13 Consider the system shown in the diagram The natural length of the spring is 2 2 L The system is rotated with constant angular speed The mass of the ring is M The whole system is just in equilibrium What is the minimum friction coefficient between the ring and the L shaped structure Take KR MR Mg 2 a 1 2 b 1 3 c 1 4 d 1 A 3 rrrrrrrr L Spring constant of the spring is K

1 A string is passing over a rough immovable pulley having coefficient of friction as shown in figure What should be minimum value of F to keep the block in equilibrium at rest Use e 025 0 78 2 wwww F

14 A road is banked at angle 45 as shown The car at height H experiences maximum friction force in the upward direction and the car at height experiences maximum friction force in the downward direction Both the cars are moving with the same angular velocity about the same axis of rotation If the size of cars is considered to be negligible then find out the coefficient of friction between the road and the tyres Both the cars have the same tyres and therefore same value of coefficient of friction 45 H 2H

4 A body is moving with a velocity of 72 km hr on a rough horizontal surface of coefficient of friction 0 5 If the acceleration due to gravity is 10 m s find the minimum distance it can be stopped a 20 m b 40 m c 10 m d 30 m 2007

A wedge is moving with acceleration a towards left as shown such that block placed on it remain at rest with respect to it If the coefficient of friction between the block and the wedge is 0 5 The ratio of maximum to minimum value of a for this to happen is 45 A 4 B 6 C 9

This section contains EIGHT 08 questions The answer to each question is a NUMERICAL VALUE For each question enter the correct numerical value of the answer in the place designated to enter the answer If the numerical value has more than two decimal places truncate round off the value to Two decimal places eg 6 25 7 00 0 33 30 30 27 127 30 if answer is 11 36777 then both 11 36 and 11 37 will be correct Answer to each question will be evaluated according to the following marking scheme Full Marks 3 If ONLY the correct numerical value is entered Zero Marks 0 In all other cases A curved road with radius of curvature 500 m is banked with an angle of bank equal to tan 0 5 If the velocity of car is 3 times the bank velocity the minimum friction coefficient required is given by u Find the value of

9 kg 35 kg Block B of mass 7 kg is resting on it as shown on a frictionless floor Its mass is in the diagram The co efficient of static friction between the block and slab is 0 5 While kinetic friction is 0 4 Force F is applied to the block B g 10ms 2 B m A m F The minimum value of force F to cause block B to move with respect to slab A is 1 72 N 2 42 N 3 35 N 4 none D In above problem if m 10kg m 40 kg and applied force is 40 N the acceleration of the block B with respect to slab A will be 1 zero 2 0 5 ms 2

A block of mass 2 kg is kept on a horizontal floor as shown Coefficient of static friction between the block and the ground is 0 3 The block will not move no matter how large the force F in N is if F k find k 0 3 2 kg

Two blocks A and B having masses 5 kg are connected by a massless string and are place on a horizontal plane as shown in figure If B pulled by 8 N horizontally then tension in string g 10 m s2 A 5kg 0 2 B 3kg 0 3 8N

Questions asked Prior to Medical Ent Exams 2005 A charged cloud system produces an electric field in the air near the earth s surface A particle of charge 2x 10 9 C is acted on by a downward electrostatic force of 3 x 10 6 N when placed in this field The gravitational and electrostatic force respectively exerted on a proton placed in this field are 1 1 64 x 10 26 N 2 4 x 10 16 N X 2 1 64 10 26 N 1 5 10 N 3 1 56 10 18 N 2 4 x 10 16 N 4 15 x 10 N 24 x 10 16 N vel

A trolley of mass 20 kg rests on a horizontal surface A massless string tied to the trolley passes over a frictionless pulley and a load of 5 kg is suspended from the other end of string If coefficient of kinetic friction between trolley and surface is 0 1 find the acceleration of trolley and tension in the string Take g 10 ms

Q40 A spring block system is resting on a frictionless floor as shown in the figure The spring constant is 2 0 N m and the mass of the block is 2 0 kg Ignore the mass of the spring Initially the spring is in an unstretched condition Another block of mass 1 0 kg moving with a speed of 2 0 m s collides elastically with the first block The collision is such that the 2 0 kg block does not hit the wall The distance in metres between the two blocks when the spring returns to its unstretched position for the first time after the collision is 2018

A block of mass m is placed on a prism which can slide on a horizontal surface The inclined surface of the prism on which block is placed is rough With what acceleration the prism is to be accelerated horizontally So that force of friction on the block can be zero The angle of inclination of the prism is and the acceleration due to gravity is g

ALLER 1 A light string passing over a smooth light 21 pulley connects two blocks of masses m and m2 vertically If the acceleration of the blocks is g 8 then the ratio of the masses is 1 8 1 2 9 7 3 4 3 245 120137 93 Eu Rela Ell is a g 1 8 1 2 9 7 3 4 3 4 5 3

11 In the shown figure the maximum value of horizontal force F for which both the blocks move together without slipping between them is take g 10 m s 1 25 N 3 35 N F 2 Kg 5 Kg 0 3 0 2 2 30 N 4 40 N

The blood flows through a large artery ex from heart to lungs with a radius of 2 5 mm and 15 cm long The pressure across the artery ends is found to be 380 Pa then what is the blood s average speed Coefficient of viscocity of blood is 0 0027 Poiseulli 1 0 0286 mm s 3 0 0073 mm s 2 0 0144 mm s 4 0 00073 mm s 2

3 135 J 4 90 J 20 On the horizontal surface of a truck a block of mass 2 kg is placed If the co efficient of friction for the contact is 0 6 and truck is moving with 2 m s then the frictional force on the block will be 1 5 N 3 6 N 2 4 N 4 5 88 N

Friction depends upon of the surfaces in contact and is indepe of the surfaces in contact O area and shape nature and material Onature and material area and shape O area smoothness Onone of these

block of mass 10kg is placed on a rough horizontal ground A force of 40N is applied on the Bock as shown in figure The block with constant velocity 10m s in opposite direction of the pplied force F Then take g 10m s 10kg F 40N

18 In the arrangement shown three loads are suspended in equilibriur from three pulleys The segment of the rope between each of th uppermost pulleys and the outermost pulleys leans at angle with th vertical a What is the ratio of masses m M b Find range of coefficient of friction between the walls and th outermost pulleys c What is the nature of the equilibrium

5 A block moving on a rough horizontal surface comes to rest after moving for a time to The ratio of work done by the force of friction in first half time to that in next half time is 1 1 3 3 1 1 2 3 1 4 2 1

Two blocks having same mass are placed on rough incline plane and the coefficient of friction between A and incline is 1 0 and between block B and incline is 2 As the inclination of the plane 0 with respect to horizontal increases Choose the correct answers s BA B there is no contact force between block A and B as 0 30 there is no contact force between blocks A and B as 0 45 both the blocks have same accelerations 1 1 2 they starts moving at an angle tan

d None of these 49 A block of mass m remains stationary on a fixed incline plane of inclination 0 If u coefficient of static friction the reaction of ground on the block is a mg cos 0 c mg sin 8 b mg cos 07 d mg

3 A galvanometer having a coil resistance of 100 gives a full scale deflection when a current of 1 mA is passed through it The value of the resistance which can convert this galvanometer into ammeter giving a full scale deflection for a current of 10 A is JEE Main 2016 1 292 3 39 2 0 192 4 0019

A chalk block of mass 2kg is given an initial speed of 2 m s along a rough horizontal floor u 0 2 Due to wear the block loses mass at a constant rate of 0 1 kg m The block finally comes to rest covering k meters before it stops Find k

3 A child is swinging on a swing Minimum and 38 maximum heights of swing from earth s surface are 0 75 m and 2 m respectively The maximum velocity of this swing is 1 5 m s 2 10 m s 3 15 m s 4 20 m s 16X

3 Two blocks of mass m of mass m 3 kg and m kg connected by a light inextensible string which pas over a smooth peg The peg is fixed on the top wedge The planes of the wedge supporting m m are inclined at 30 and 60 respectively with of

A pendulum of length is free to oscillate in vertical plane about point O An observer is viewing the bob directly from above The pendulum is performing small oscillations in a liquid of refractive index The equation of bob as seen by observer is best given as Itals i c dug fag og da fay zada 21 yg du 42 mac ch tu za 21 duga uadaich a 34 da ta he 25 1 uh Az Tu s as zu A x y 1 B C D y 7 1 2 x y Your Answer 1 72 X

Mark the incorrect statement about the friction between two bodies 1 Static friction is always greater than the kinetic friction 2 Coefficient of static friction is always greater than the coefficient of kinetic friction 3 Limiting friction is always greater than kinetic friction 4 Limiting friction is never less than static 34 35

1 A 2 B 3 C 4 D 14 The blocks are in equilibrium The friction force action on 10 kg block is boks 0 5 1 10 N down the plane 2 40 N up the plane 3 10 N up the plane A 40 N down th plane

Mg sin 1 sin 0 3 A block is projected with speed 20 m s or rough horizontal surface The coefficient friction between the surfaces varies w time t as shown in figure The speed of bo at the end of 4 second will be g 10 m s The 1 2 m s 3 7 2 m s 0 5 0 3 4 Mg sin 2 7 2 t s 2 5 m s 4 9 5 m s steing choum in fou

3 Two blocks A and B of masses 5 kg and 3 k respectively rest on a smooth horizontal surfac with B over A The coefficient of friction A an B is 0 5 The maximum horizontal force in k wt that can be applied to A so that there will b motion of A and B without relative slipping i 1 1 5 2 2 5 3 4 4 5

In the figure shown horizontal force F is applied on a block but the block does not slide Then as the magnitude of vertical force F is increased from zero the block begins to slide the correct statement is 1 The magnitude of normal reaction on block increases 2 Static frictional force acting on the block increases 3 Maximum value of static frictional force decreases 4 All of these

4 The materials of the bodies A horizontal force 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 F 10 N Wall 1 20 N 2 50 N 3 100 N 4 2 N