Friction Questions and Answers

Question 23 Consider uniform cubical box of side a on a rough floor that is to be moved by applying minimum possible force F at a point b above its centre of mass see figure If the coefficient of friction is 0 4 the maximum possible value of 100 b a for box not to topple before moving is

As shown in the figure below the tank is filled with 100 1 water and it has inlet pipe with filling rate of 1250 ml minute A bucket is attached to the tank with the help of frictionless pulley bucket is filled with 50 I but it has outlet pipe with leaking rate of 750 ml minute Take angle of plane as 20 and coefficient of friction as 0 30 Calculate at what time tank will slip down 11 1000ml and 1 1 1kg take g 10 m sec fill rate 1250 ml minute Tonk 1001 M 0 30 friction less pulley 506 Bucket leak rate 750ml

A given object takes 2 times as much time to slic down a 45 rough incline as it takes to slide down perfectly smooth 45 incline The coefficient kinetic friction between the object and the incline given by 1 3 4 2 4 3 4 4 1

lative lume if the ty of nis on is an is 2 2 an fic T ere he ass ter K e a 6 5 28 A stone is thrown horizontally with velocity The velocity of the stone 0 5 s later is 3u 2 The K value of u is a 2 2 ms c 4 4 ms 29 The dimension of the quantity mtG Objective NCERT b 5 6 d 4 5 a M L T A c ML T A2 b 3 3 mg d 1 1 ms 1e to he electron Planck s constant and c velocity of light b MOLTA d M L TA a 4 1 c 3 1 is e chargest 30 A projectile is thrown with an initial velocity a b ms where and are the unit vecton along horizontal and vertical directions respectively If the range of projectile is twice the maximum height reached by it then a b 2 c b 2a b b a d b 4a 31 A uniform wire of length 20 m and weighing 5 kg hangs vertically If g 10 ms2 then the speed of transverse waves in the middle of the wire is a 10 m 5 c 4 m s b 10 2 ms d 2 ms 32 The velocity of a body moving in a vertical circle of radius r is 7gr at the lowest point of the circle What is the ratio of maximum and minimum tension b 7 1 d 2 1 33 Figure shows position and velocities of two particles moving under mutual gravitational attraction in space at time t 0 YA 2 kg 8ms 2ms 13 kg r 2m x 12 m The position of centre of mass after one second is a x 4m b x 6 m c x 8m d x 10 m 34 How large must Fbe in the figure shown to give the 700 g block an acceleration of 30 cm s The coeff icient of friction between all surfaces is 0 15 Poctice Paper 2 a 2 18 N c 4N The radii of two columns in a U tube are r and r When a liquid of density p angle of contact is 0 is filled in it the level difference of liquid in two arms ish The surface tension of liquid is g acceleration due to gravity pghr 2 1 1 2 5 pghr c cos c 36 The angle subtended by the vector 41 3 12k with the x axis is a sin b sin c PV c T RT 200 g 20 T 700 g b 3 18 N d 6 N 37 A solid cylinder rolls without slipping down a 30 slope The minimum coefficient of friction needed to prevent slipping will be a 0 192 c 0 15 b 0 18 d 0 2 RT S b 38 The equation of state for 5 g of oxygen at a pressure P and temperature T when occupying a volume V will be a PV S d pgh 27 72 pgh 2 7 7 d cos 3 b PV 5RT d PV 39 A weightless spring of length 60 cm and force constant 100 N m is kept straight and unstretched on a smooth horizontal table and its ends are rigidly fixed A mass of 0 25 kg is attached at the middle of the spring and is slightly displaced along the length The time period of the oscillation of the mass is a b d 16 RT 10 40 A T m 05 41 T 200 an ta 47

A box of mass 20 kg is connected to mass of 2 kg hanging through a light string and an ideal pulley as shown in figure Coefficient of kinetic friction between trolley and surface is 0 05 What is acceleration of the box g 10 m s 20 kg Box 4 11 m s 2 5 11 m s 6 11 ms 2 2 kg

A horizontal force of 100 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 1 20N 2 2N 100 N 4YSN

Starting from rest a body slides down a 45 inclined plane in twice the time it takes to slide down the same distance in the absence of friction The coefficient of friction between the body and the inclined plane is 1 0 33 2 0 25 3 0 75 4 0 80

A 1 5 kg cart is pulled with a force of 7 3 N at an angle of 40 above the horizontal If a kinetic friction force of 3 2 N acts against the motion the cart s acceleration along the horizontal surface will be a 2 7 m s b 2 4 m s c 1 6 m s d 5 0 m s

Static friction between two surfaces Prevents the relative motion between them Acts opposite to the direction of motion of them and is constant Acts in opposite direction of applied force Both 1 2

A uniform cubical block is held stationary against a rough wall by applying a force F then which of the following statement is correct 2a Ta F 1 Normal reaction will pass from the center of cube 2 Normal reaction will act above the centre 3 Normal reaction will pass below the center 4 Torque of friction will be zero about the center of the cube

Coefficient of friction between A and B is u The minimum force F with which A will be pushed such that B will not slip down is AMN A 1 3 M B Frictionless Mg H M m g 2 4 mg 7 FE M m g my AN N M

Identify the correct statement Kinetic friction depends on area of contact for a given normal contact face Coefficient of kinetic friction is generally less tha coefficient of static friction The magnitude of kinetic friction cannot be more than static friction Coefficient of static friction does not depend on surface nature in contact

26 A suitcase is gently dropped on a conveyor belt moving at 3 m s If the coefficient of friction between the belt and the suitcase is 0 5 Find Find the displacement of suitcase relative to conveyor belt before the slipping between the two is stopped g 10 m s a 2 7 m c 0 9 m b 1 8 m d 1 2 m

A small block of mass m can move inside a fixed spherical rough surface of radius R Block is given a horizontal velocity V at lower most point sufficient for block to complete one round of vertical circular motion Choose the CORRECT statement s for first round of vertical circular motion R B A Work done by friction in part AB is equal to that in part DA B Work done by friction in part ABC is greater than that in part CDA C Velocity at point B must be greater than 3gR D Velocity at D is equal to velocity at B

A block D weighing 300 kg is suspended by means of two cords A and B as shown in the figure W is a vertical wall and R a horizontal rigid beam The tension in the string A in kg is R W zero 150 300 90 A 45 D 300 kgf CORRECT ANSWER

blocks of masses and 8 kg The blocks A B 3 kg 4 kg respectively are placed another over one F C Fig 2 27 Coefficient of friction Fig 2 27 between each pair of surfaces in contact is 0 25 A connected to the wall by a massless rigid rod B a C are connected by an inextensible thread passin over a rigidly fixed smooth pulley Find the force

Q NO 6 A block of weight 5 kN is pulled by a force P as shown in Fig The coeficient of Friction between the Contact surfaces is 0 35 Find the direction for which P is minimum and corresponding P 0 P

4 Two particles 1 and 2 are allowed to descend on two frictionless chords OP P18 and OQ The ratio of the speeds of the particles 1 and 2 respectively when they reach on the circumference is c 1 d a 1 4 1 0 2 1 2 2 2 Q Laro

Put a uniform meter scale horizontally on your extended index fingers with the left one at 0 00 cm and the right one at 90 00 cm When you attempt to move both the fingers slowly towards the centre initially only the left finger slips with respect to the scale and the right finger does not After some distance the left finger stops and the right one start slipping Then the right finger stops at a distance xR from the centre 50 00 cm of the scale and the left one starts slipping again This happens because of the difference in the frictional forces on the two fingers If the coefficients of static and dynamic friction between the fingers and the scale are 0 40 and 0 32 respectively

A ball collides perfectly inelastically with smooth horizontal ground at angle 30 with vertical as shown Fraction of kinetic energy lost by the ball due to collision is Ball 30 Smooth Horizontal Surfao

A smooth inclined plane is making an angle 30 to the horizontal a rough plane of same length is held at 45 A body released from the top of each inclined plane reaches the bottom after the same time Then coefficient of friction for that body ad the rough plane is 2 1 1 T2 1 2 2 1 2 3 2 1 4 None

Ex 2 If a hemisphere rests in equilibrium with its curved surface in contact with a rough plane inclined to the horizon at an angle a Show that the inclination of the plane base of the hemisphere to the 1 horizontal is sin 8 3 sin a provided that a sin 3 8 and a 2

3 A dc series generator has armature resistance of 0 52 and series field resistance of 0 0352 It drives a load of 50A If it has 6 turns coil and total 540 coils on the armature and is driven at 1500 rpm calculate the terminal voltage at the load Assume 4 poles lap winded flux per pole is 2mwb and total brush drop as 2V

Area of tube is A and is very small in comparison of container Due to ejection of water density p at a velocity v the spring is compressed as shown in figure The compression in spring at the given instant is if container is in rest positions 00000 Option A B pv A 2K pv A K Rate this question

A wedge of mass M 10kg and inclination a 30 is free to move on a smooth horizontal plane A uniform solid cylinder of mass m 20 kg is placed on the rough inclined face of the wedge Find the acceleration in m s2 of the centre of the cylinder relative to the wedge down the face There is no slipping between the cylinder and the wedge

A body of mass 60 g is kept on an inclined plane of inclination 30 If the downward resultant force is 0 1764 N estimate the value of the coefficient of friction 0 23

A block of mass m rests on a rough horizontal surface as shown in figure a and b Coefficient of friction between the block and surface is u A force F mg act at an angle 0 with the vertical side of the block Find the condition for which the block will move along the surface m 6 F mg b F mg m

What is the flaw in Aristotle s argument The answer is a moving toy car comes to rest becaus the external force of friction on the car by the floc opposes its motion To counter this force the chil has to apply an external force on the car in th direction of motion When the car is in unifor motion there is no net external force acting on the force by the child cancels the force frictic

Each of the three plates has a mass of 10 kg If the coefficients of static and kinetic riction at each surface of contact are us 0 3 and k 0 2 respectively determine the cceleration of plate C m s2 when the three horizontal forces are applied F 108 N 9 81 m s Note Please write only 3 digits after the comma 18 N 15 N D C B F N

5 A wire of length 1m placed in x z plane carries a current of 1 amp The coefficient of friction between the wire and the surface is 0 2 and mass of the wire is 2 kg The magnetic field of strength 2 T exists along positive y direction Then choose the correct statement a Acceleration of wire is 0 5 m s b Wire will not move at all c Acceleration of wire is m s d Acceleration of wire is 2m s

A block of mass m 2 kg is resting on a rough inclined plane of inclination 30 as shown in figure The coefficient of friction between the block and the plane is 0 5 What minimum u force F should be applied perpendicular to the plane on the block so that block does not slip on the plane g 10m s Question Type Single Correct Type 1 zero 2 6 24 N 30 3 2 68 N

c 0 1mg Asmg 0 Two blocks A and B of masses 10 kg and 15 kg are placed in contact with each other rest on a rough horizontal surface as shown in the figure The coefficient of friction between the blocks and surface is 0 2 A horizontal force of 200 N is applied to block A The acceleration of the system is Take g 10 m s2 a 4 ms2 b 6 ms c 8 m s 200 N A B

A uniform ladder AB whose weight is 600 N and length 4 metres rests against a smooth vertical wall making with it an angle of 30 The other end rests on the ground surface Find the reactions given to the ladder by the wall and the floor and their inclination to the vertical when a man weighing 700 N climbs the ladder by a distance 1 5 m along the length of the ladder

16 The system is pushed by a force Fas the figure All surfaces are smooth except between B and C Coefficient of friction between B and C is u Minimum value of F to prevent block B from downward slipping is A B C 2m 1 3 T 3 2 5 2 F mg umg 2m 2 4 m 5 2 3 2 mg umg

Consider an ice skater gliding on ice holding bag of sand that is leaking straight down with respect to the moving skater As a result of the leaking sand the speed of the skater Group of answer choices Not enough information is given to decide does not change increases

2 In the figure shown a force of 40 N is applied on the plank of mass 5 kg A solid sphere of mass 3 kg rolls without slipping on plank 1 O 3 Choose the correct answer 1 Acceleration of plank is 20 13 40 13 m s 3 kg m s 5 kg 40 N 30 2 13 4 83 20 m s m s

A block of mass 1 kg is placed on the periphery of a rotating rough circular table of radius 50 cm as shown in the figure Angular velocity of the table is 4 rad s The minimum value of coefficient of friction between the contact such that there is n relative slipping is g 10 m s 0 8 1 6 0 4 0 2

Object 2 with mass 1 3kg is at rest on rough surface k 0 45 connected to a cord over massless frictionless pulley to object 1 with mass 10kg what is the magnitude of the system acceleration in m s N 6 30 9 50

A metallic sphere of mass 3 kg in air is held by a string so as to be completel immersed in a liquid of relative density 0 8 The relative density of metallic sphere is 10 The tension in the string is g 10 m s 2 O O c 18 7 N 42 5 N 32 7 N 27 6 N

A bus turns on an unbanked rough road having coefficient of friction 0 4 with a speed of 5 m s The minimum radius of the arc in which bus turns safely without skidding is Take g 10 m s 12 5 m 6 25 m 15 m 20 m

R 9 Option D Consider a rope of mass 4m and length 4R on a fixed rough pulley of radius R as shown in the figure The rope is in equilibrium Length of vertical hanging parts is shown in the figure C B A 2R Torque of tension force about O on pulley is 4mgR Torque of normal force between rope and pulley on pulley about O is zero Rate this question Torque of friction force between rope and pulley on pulley about O is mgR Torque of friction force between rope and pulley on pulley about O is zero

012 10 0 points It takes 2 84 J of work to stretch a Hooke s law spring 5 58 cm from its unstressed length How much the extra work is required to stretch it an additional 13 5 cm Answer in units of J

1 2 Given graph is a plot of magnitude of normal limiting friction kinetic friction and static friction versus angle of inclination 0 for the coin lying on book 17 points are labeled with numbers The coin slips at a certain angle 0 The coefficient of static friction is 0 6 and the coefficient of kinetic friction is 0 4 0 is given by point A 14 4 B 15 Force 10 Jungle Book 14 13 15 16 17 Angle 0 The magnitude of the normal force on the coin from the book A 6 B 2 C 7 C 16 5 D 11 D 17

For what value of P the point 1 1 2 3 and P 2 will form an isosceles right angled triangle Pfag farg 1 1 2 3 3 P 2 B 1 A 0 OA C 4 D 2

A block of mass 1 kg is found to be moving with velocity 10j m sec on rough horizontal surfac xy plane u 0 2 which is also moving with velocity 101 m sec The smallest angle made by friction acting on block with positive x axis is given by a T Fill the value of 12 a in OMR sheet

Section 1 Straight Objective Type This section contains 5 multiple choice questions Each question has 4 choices a b c and d out of which ONLY ONE is correct 1 Three blocks A B C of weights 40N 30N 80N respectively are at rest on an inclined plane as shown in figure Determine the smallest value of coefficient of limiting friction u for which equilibrium of system is maintained a 0 1757 b 0 2757 c 0 5757 d 0 8757

A circular tube of mass M is placed vertically on a horizontal surface as shown in the figure Two small spheres each of mass m just fit in the tube one released from the top If the tube looses contact with the ground at 60 then the value of M m Option A mim o B 2 11 13 M Rate this question

c 6 ms 2 d 8 m s 53 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 s2 The frictional force acting on the block is a 10 N b 5 N c 2 5 N d 20 N A block of mass 2 kg rest on a plane inclined at an

c T m d 0 74 The mass of a bicycle rider along with the bicycle is 100 kg He wants to cross over a circular turn of radius 100 m with a speed of 10 m s If the coefficient of friction between the tyres and the road is 0 6 the frictional force required by the rider to cross the turn is a 300 N c 1200 N 75 A stone of m b 600 N d 150 N

a 10 N b 5 N c 2 5 N d 20 N a c 54 A block of mass 2 kg rest on a plane inclined at an angle of 30 with the horizontal The coefficient 70 T of friction between the block and the surface is 0 7 What will be the frictional force acting on the block a 10 3 N b 23 8 N c 11 9 N d 6 3 N A block of mass M is held against a rough vertical P h 43 C