Friction Questions and Answers

In a laboratory experiment on friction a block of weight 135 N lying on a rough horizontal table is pulled by a horizontal wire The pull P gradually increases until the block begins to move and continues to increase thereafter Given figure shows a graph of the friction force on this block as a function of the pull P The regions of the graph where the static friction occur is from f N 75 50 25 0 25 50 75 100 1 P ON to P 100 N 2 P 0 N to P 75 N 3 P 75 N to P 100 N 4 Only at P 75 N P N

A uniform chain of length L is resting on a table with a part of its hanging over the edge If the coefficient of static friction between the chain and the table is u the maximum length of the hanging part is 1 3 UL 1 1 L 1 UL 2 1 4 L

10 Friction between rigid rod of mass m and wedge of mass 2m is zero while coefficient of friction between ground and wedge is 0 1 A force F is applied on the wedge so that rod moves with constant velocity v 5 m s in upward direction as shown The power delivered by force F will be W take m 1 kg g 10 m s No THE 0 1 Rod 37 m wedge 2m F TT

Two blocks are placed over an inclined plane as shown in figure Masses and the coefficient of friction between the surfaces are shown in figure Now if 0 is increased slowly till the time when there is no sliding between any two surfaces if 0m is the maximum possible value of then the value of N is angle and tan 0m 0 2 kg 4 kg 0 2 0 3

A block of mass m is placed over rough plank of mass 2m and length 1 m and complete system is placed over smooth horizontal surface as shown in figure If block is given velocity vo 2 m s then choose the correct options Smooth m m 1 kg Vo 2m 0 1 Velocity of block at the time of leaving plank is 1 m s Velocity of plank at the time block leaves it is 1 m s Velocity of block at the time of leaving plank is 4 m s IN Block will leave the plank after time 2 S

2 11 A block rests on a rough pl horizontal can be varied Which of the following graphs indicates how the frictional force F between the block and the plane varies as 0 is increased A C FA FA b 90 0 B FA D 0 si no abnogob a b F 90 0

A small block of mass of 0 1 kg lies on a fixed inclined plane PQ which makes an angle with the horizontal A horizontal force of 1 N on the block through its center of mass as shown in the figure and the block remains at rest When take g 10 m s C 1N P e 40 frictional force acts on the block towards P e 50 no frictional force acts on the block 6 30 frictional force acts on the block towards Q e 60 frictional force acts on the block towards Q

The upper block is given a sudden velocity of 10m s After what time both the block starts moving together and net work done on system upto that instant lower block is long enough u 0 4 A Isec 62 5 J C 125 25 sec 5kg 5kg 125 J V 10m s Smooth B 2 25 sec 125 J 1 25 sec 625 I

In the given figure if galvanometer deflection then emf of each cell will be 5 V 12 1 9 V 3 45 V A 2 m E E 10 m 99 B 2 0 9 V 4 18 V

Two blocks A 4 kg and B 6 kg rest one over the other on a smooth horizontal plane The coefficient of static and dynamic friction between A and B is the same and equal to 0 3 The maximum horizontal force F that can be applied to B in order that both A and B do not have any relative motion is 1 30 N 0 3 F A B 4 kg 6 kg 2 2 30 kgf san

A block of mass 2 00 kg is moved up a 30 0 rough incline a distance of 3 00 m starting from rest A spring with spring constant of 100 N m is fastened to the top of the incline as shown in the figure A force of F 15 0 N is acting on the block at an angle of 40 with the horizontal a How much work is done by the gravitational force on the block 1 point b How much work is done by the normal force on the block 0 5 point c How much work is done by the 15 0 N force on the block 1 point d Calculate work done by the friction force on the block 1 point e Calculate the speed of the block right before touching the spring 1 point f The block compresses the spring by x and stops momentarily before it is pushed down by the spring Find the compression of the spring x 1 point 0 30 3m M 0 3

0 A block of mass 1 kg lies on a horizontal surface in a truck The coefficient of static friction between the block and the surface is 0 6 If the acceleration of the truck is 5 m s 2 The frictional force acting on the block is 1 10 N 2 5 N 3 2 5 N 4 20 N

3 1 tan 0 A person stands in contact against the inner wall of a rotor of radius r The coefficient of friction between the wall and the clothing is u and the rotor is rotating about vertical axis The minimum angular speed of the rotor so that the person does not slip downward is ur 1 g 2

A block is placed on a rough horizontal surface The minimum force required to slide the block is u is coefficient of friction between the contacting surface 1 Fcose umg 0 M 0 7F 2 mg A umotanA

6 If a body of mass m is moving on a rough horizontal surface of coefficient of kinetic friction the net electromagnetic force exerted by surface on the body is 1 mg 1 4 3 mg 2 mg 4 mg 1

A block is lying static on the floor The maximum value of static frictional force on the block is 10 N If a horizontal force of 6 N is applied to the block what will be the frictional force on the block 2 18 N 1 2 N 3 6 N 4 10 N

stion 7 A motor car moving at a speed of 72 km h canne s less than 3 0 s while for a truck time interval is 5 0 s Or r is behind the truck both moving at 72 km h The t that it is going to stop at emergency At what distance th a the truck so that it does not bumb onto collide wit response time is 0 5 s

2 0kg 370 P A 2 kg block is dragged over a displacement of 4 0 meters by a constant force of P 3 N acting at an angle of above the horizontal as shown The surface is rough and a constant frictional force of f 2N opposes the motion What work was done by the frictional force f force during this displacement O 8 0 J O 6 4 J O 1 6 J 09 6 J O 12 J

A block of mass M 5 kg is resting on a rough horizontal surface for which the coefficient of friction is 0 2 When a force F 40 N is applied the acceleration of the block will be g 10 m s 1 5 73 m sec 2 8 0 m sec 3 3 17 m sec 4 10 0 m sec M F 30

The small sphere of mass m is suspended from a rigid support s with the help of an inextensible string of length 1 The small sphere is given a horizontal velocity v 2g and left to move in vertical plane The acceleration of bob when the string makes an angle of 60 with the lower vertical direction is S 1 m 60 v 2gl 12 2 3

A small block of mass m is placed on a plank of mass M which res a frictionless horizontal floor Coefficient of friction between the and the plank is The block is given a sharp impulse so that it sliding on the plank with an initial velocity u Due to friction bet the block and the plank the block slows down and finally stops s on the plank What average thermal power is dissipated in this pr

3 kg 64 Smooth 9 kg F 27 N In the arrangement coefficient of friction between the two blocks is The force of friction acting 1 3 between the two blocks is 1 10 N 3 40 N 2 6 75 N 4 13 5 N

figure For aluminum on steel s 0 61 and 0 47 For copper on steel S Aluminum m1 Steel Copper m a the acceleration of the two blocks m s N b the tension in the string 0 53 and MK 0 36

5 Initially cylindrical drums P and Q were placed at equal distance L from center of mass C of the rough rod AB in horizontal position The drums were spinning in opposite directions with angular velocities The rod is displaced by distance x towards left and released so that it performs SHM If difference in reactions at Q and P is mgx where L m is the mass of the rod find the time period of oscillations if m is the coefficient of friction A L XL X L 1 27 g 3 2T L x 110 P C 2 2 4 2 L x L 08 B 110

24 25 of A A block of mass 1 kg lies on a horizontal surface in a truck The coefficient of static friction between the block and the surface is 0 6 If the acceleration of the truck is 5 ms The frictional force acting on the block is 1 10 N 3 2 5 N The resistance in the two arms of a meter bridge are 2 5 N 4 20 N GUI 1 far and wenzetten van en 0 6143 24 25 5 1 10 3 2 527 fare ex ig att 2 52 4 20

Two blocks of masses 10 kg and 5 kg are placed one over the other on a horizontal plane as shown in the figure If co efficient of friction is 0 2 and an external force F 45 N is applied horizontally on the lower block Then the force of friction in newton between the two blocks is 0 2 0 2 5 kg 10 kg F 45N 7777

This problem utilizes most of the important laws introduced so far and it is worth a substantial effort The problem is tricky although not really complicated so don t be alarmed if the solution eludes you A plank of length 2L leans against a wall It starts to slip down ward without friction Show that the top of the plank loses contact with the wall when it is at two thirds of its initial height 2L 0

A 5 560 kg block of wood rests on a steel desk The coefficient of static friction between the block and the desk is 0 455 and the coefficient of kinetic friction is 0 255 At time t 0 a force F 15 3 N is applied horizontally to the block State the force of friction applied to the block by the table at times t 0 and r 0 1 0 NL 0 m Hak N Consider the same situation but this time the external force F is 30 8 N Again state the force of friction acting on the block at times t 0 and 0

A person clings to a playground fire pole Firepole by Donkeysforever via Wikimedia Commons is in the Public domain Fill in the missing words and values A child with a weight of 178 N 40 lbs clings to a steel fire pole slide on a playground What static frictional force is need to support the child Static friction requires a pole to generate this N force be present so the child must squeeze the force If the coefficient of friction between skin and steel is 0 800 with what minimum force must the child squeeze the pole in order to remain in place N

A truck starting from rest moves with an acceleration of 5 m s for 1 s and then moves with constant velocity The velocity w r t ground versus time graph for block in truck is Assume that block does not fall off the truck a 5 m s c 5 m s 1 s A b 0 2 3 m s 1 s d None of these

A solid cylinder and a solid sphere of same mass and radius roll without slipping on a rough inclined plane The force of friction is 1 Same for both the bodies 3 More for sphere 2 More for cylinder 4 Double for sphere than for cylinder

If the coefficient of friction between A and B is u the maximum horizontal acceleration of the wedge A for which B will remain at rest w r t the wedge is A u g C 6 0 3 D g 1 1 wa B g 1 1 B 45 a

system of two blocks as shown in figure below is pushed by a horizontal force F on a smooth horizontal surface The coefficient of friction between blocks is u The minimum force F required to prevent slipping between the blocks is F m m fs H

5 3 5 2 4 5 3 Consider the following two statement A and B and 45 identify the correct choice in the given answers A The excess pressure inside a small liquid drop is more than that of a big drop B As the aeroplane moves fast on the runway for take off the pressure is more on the upper surface of its wings and less on the bottom surface of the wings 1 Both A and B are true 2 A is true but B is false 3 A is false but B is true 4 Both A and B are false 3 5 2 fat and t A fen arfires at th 4 5 3 Badan free f tataka watan t 1 AB 2 AB 3 A et B mit 4 AB f

A man is standing on a plank which is placed on smooth horizontal surface There is sufficient friction between feet of man and plank Now man starts running over plank correct statement is are Work done by friction on man with respect to ground is negative Work done by friction on man with respect to ground is positive Work done by friction on plank with respect to ground is positive Work done by friction on man with respect to plank is zero

NOTE Challenger from previous Tecture Find the maximum height upto which an insect can crawl up hemisphere of radius R The coefficient of friction between the leg the insect and the bowl is u tano 1 1

Shown in the figure below is a system of two blocks One of these blocks is resting on a flat surface and the other one is on an angled surface The strings and the pulley have no mass Tw T m Answer all the following friction The characteristics of the system are given here m 5 43 kg m 1 07 kg 0 30 8 64 0 What is the normal force N on mass m What is the normal force N on mass m N N

Two masses of 10 kg and 5 kg respectively are connected by a string passing over a frictionless pulley fixed to the edges of a table as shown coefficient of friction between the table and 10 kg mass is 0 4 What should be the minimum mass M which should be placed on 10 kg so as to prevent it from moving 1 15 kg A 10 kg 2 10 kg B5 kg 3 5 kg 4 2 5 kg

152 A small mass slides down an inclined plane of inclination e with the horizontal The coefficient of friction is u x where x is the distance through which the mass slides down and Mo a constant Then the speed is maximum after the mass covers a distance of cos 8 a Ho b c tan 8 Ho d sin 0 Mo 2 tan 0 Ho

31 A force of 100 N is applied on a block of mass 3 kg as shown in the figure The coefficient of friction between the surface and the block is u The frictional force acting on the block is a 15 N downwards c 20 N downwards 30 100 N 3 kg b 25 N upwards d 30 N upwards

The time taken by a block to slide down a 45 rough incline plane is n times greater than that it would take if the incline were perfectly smooth The coefficient of kinetic friction between the block and the incline is 1 171 722 1 1 n 1 Ji n

Wings on race cars push them into the track The increased normal force makes large friction forces possible At one Formula One racetrack cars turn around a half circle with diameter 190 m at 68 m s Part A For a 610 kg vehicle the approximate minimum static friction force to complete this turn is O 15000 N 6000 N O 24000 N O 18000 N O 00000 N

14 A 50 kg crate slides across a horizontal surface at constant speed when a horizontal force of 160 N is applied to it What i the coefficient of friction between crate and surface 033 0 30 0 40 0 27 0 36

6 3 1 Jennifer is pushing a heavy box up a rough inclined surface at constant speed by applying a horizontal force F as shown in th drawing The coefficient of kinetic friction for the box on th inclined surface is uk Which one of the following expression correctly determines the normal force on the box F mg tan 0 a FN k b F F mg tan 0 F cos mg sin FN Mk d F F cos 0 mg sin 0 F sin 0 mg cos e F F 0

12 A 20 m 500 N uniform ladder rests against a friction less surface making an angle of 600 with the horizontal when an 850 N fire fighter is 5 0 m from the bottom a Find the horizontal and vertical forces exerted on the base of the ladder by the ground 6 points

3 A boy pulls a 29 0 kg box with a 180 N force at 37 above a horizontal surface If the coefficient of kinetic friction between the box and the horizontal surface is 0 27 and the box is pulled a distance of 26 0 m what is the net work done on the box

4 A roller coaster reaches the top of the steepest hill with a speed of 6 80 km h It then descends the hill which is at an average angle of 40 and is 54 0 m long What will its speed be when it reaches the bottom Assume HK 0 20 m s

30 4 0 kg 0 18 Note the 6 0 kg mass is accelerating down whereas the 4 0 kg mass is accelerating up the incline on a surface with a coefficient of sliding friction of 0 18 The equation which best describes the motion of the 4 0 kg mass if a 0 and Fr 0 is OFT 4 0x 9 8 sin 30 F 4 0 a OFT 4 0x 9 8 cos 30 F 4 0 a 6 0 kg FT4 0 x 9 8 F 4 0 a Jhry OFT 10 0 x 9 8 sin 30 F 10 0 a 4 0 x 9 8 sin 30 FTF 4 0 a

Task 2 Loading my U Haul cargo van Due date June 8 2022 You are moving into a new place and you rented a U Haul cargo van to transport your home furniture and different boxes Moving the boxes from the house to the van is done through a dolly you are using However the dolly has broken during a move There are still several boxes which must now be carried manually from the home to the van The ramp leading into the mover s van is at a 30 angle to the ground You are carrying a box weighing 200 N from the house You are placing the box on the ramp planning to push it the rest of the way into the van a Given the diagram below use arrows to indicate the directions of the frictional force the gravitational force and the normal force perpendicular to the incline of a box sitting on a ramp 3C b You can push the box with a force of 200 N parallel to the ramp but the box does not move Determine 6K i the components of the weight parallel to and normal to the direction of the ramp

as shown in the diagram at the right Which vector best represents the force of friction on the box A B