Friction Questions and Answers

A student decides to move a box of books into her dormitory room by pulling on a rope attached to the box She pulls with a force of 135 0 N at an angle of 19 0 above the horizontal The box has a mass of 25 0 kg and the coefficient of kinetic friction between box and floor is 0 300 a Find the acceleration of the box m s2 up the incline b The student now starts moving the box up a 10 0 incline keeping her 135 0 N force directed at 19 0 above the line of the incline If the coefficient of friction is unchanged what is the new acceleration of the

ER ENSTREDIE 16 A girl horizontally press her physics text book against a rough vertical wall with her hand The direction of the frictional force on the book exerted by the wall is 1 downwards 2 upwards

15 A body takes time t to reach the bottom of a inclined plane of angle 0 with the horizontal I the plane is made rough time taken now is 2t Th coefficient of friction of the rough surface is 2 tan 6 1 tan 0 4 3 1 tan 0 tan 0

A car having mass m is moving on a ro surface with momentum P If coefficien friction between tyres of car and road is u then distance covered by car before coming to r p 2 mg 1 3 P 2 mg P 2 m g 2 N p 2 m g

tan 0 1 tan 0 1 Consider the situation as shown T maximum value of force F such that the blan does not move 1 5 N 3 15 N 60 3 kg 2 3 2 10 N 4 20 N

Graph shows the relation between force applied and friction force acting on a block of mass 10 kg placed on a rough horizontal surface If coefficient of static friction is u the value of 6 will be Friction force 50N 45N Applied force Friction m F applied

2 5 A chain of mass M and length L is put on a rough horizontal surface and is pulled by constant horizontal force F as shown in figure Velocity of chain as it turns completely Coefficient of friction OOX XXX 889 F 2 15 2F 1 2 F 2 15 4 g M 2 2 2F M 4F g 2

Two blocks of masses 2 kg and 1 kg are conected and are at rest on a rough floor as shown in the figure with different coefficients of friction A 8 10 m s force of 12 N is applied on 1 kg mas as shown Let the maximum frictional force be acceleration of the system max tension in string T and the fictional force between 2 kg and floor f Then 2 kg M 0 4 1 kg 1 0 5 12 N

The body of mass m 0 5 kg is held on a vertical wall by a force F of 15 N as shown in the figure is applied on the body at an angle a 53 to the vertical Figure The coefficient of friction between the body and the wall is u 0 5 Determine acceleration of the body in m s

A force F 2t where t is time in seconds is applied at t 0 sec to the block of mass m placed on a rough horizontal surface The coefficient of static and kinetic friction between the block and surface are and respectively Which of the following graphs best represents the acceleration vs time of the block H HK A a a B K V C a MST MK D a m F 2t

4 Clamping the rod at B and applying a force F at A perpendicular to rod A solid cylinder is rolling up without sliding on a rough inclined plane The frictional force acting on it is 1 Upward along the plane 3 zero 2 Downward along the plane 4 All may be correct

The value of frictional force and acceleration of block of mass 10 kg in the figure are 10 kg 0 4 60 Question Type Single Correct Type 1 10 N 1 m s 2 20 N 2 m s 3 20 N 0 m s 4kg 4 10 N 0 m s v

A variable force 5t N is applied on a block as shown in figure where t is time in second If coefficient of 1 then find the time in sec at which block just starts to friction force between block and surface is move m 6kg F 5t

A constant horizontal force F is acting on block A as shown in the figure Friction between A horizontal surface is negligible But friction is present between A B Contact surface of A B is vertical Due to friction there is no slipping between A B Mass of A is 2m and that of B is m value of F is 6 mg Then F A B A Friction force on B must be greater than mg B Coefficient of friction between A B must be greater than or equal to 0 5 C Coefficient of friction between A B may be 0 8 D Friction force on block B may be greater than mg

Paragraph for Question No 5 to 7 A small block B of mass 10 kg is placed on a 6 m long plank A of mass 20 kg which is placed on frictionless horizontal ground Initially the block B is near the right end of plank A and the system is i rest When a constant horizontal force F of 210 N is applied to the plank A the block B falls off in 2 s Use g 10 m s GMY F A B Speed of the block B relative to the ground when it falls off the plank is em le towards loft P 9 m s towards right C 10ml towerdo loft D 10m s towards right

3 31 In the given circuit the switch is closed at t 0 The ratio of electric current through resistance R at t 0 and at t is 3 3 2 1 2 R R wwwww www R R 2 4 34 2 3 elele www R R

A horizontal force F is applied on block B as shown in the figure Now m 5 kg mg 15 kg H 0 3 0 1 Ms 0 5 0 4 Magnitude of limiting frictional force on A 15 N Magnitude of limiting frictional force on B 100 N through the ground If F 50 N then frictional force between A and B is zero If F 110 N then frictional force between A and B is 25 N

The angle between two vectors R 1 k and S xi 3j x 1 k A Is obtuse angle C Lies between 60 and 120 B Is acute angle D Depends on x

A block of mass m is initially at rest on horizontal floor having static friction coefficient us and kinetic friction coefficient is uk If F is the minimum force required to move the block then m A Value of F does not depends on us C Value of F does not depends K B Value of F does not depends m s mg 1 D F is slightly less than

A block is given a initial push along rough horizontal fixed table surface and after some time it stops due to friction For the system of block and table Question Type Single Correct Type temperature increase 2 heat supplied is positive heat supplied is negative 3

In the figure shown a hemisphere is moving in the right direction with uniform velocity Vo and the end of rod in contact with ground is moving towards left with velocity vo For the instant shown Vo B R Vo

A resultant force of magnitude 74 6 N acts on an object causing it to accelerate with a magnitude of 1 40 m s2 What is the mass of the object in units of kilograms QUESTION 8 An 856 N box rest at a horizontal floor with a coefficient of static friction us 0 75 What minimum horizontal force is required to start the box moving 117 N 642 N 1141 N 856 N

A block of mass 1 kg is placed on a board The board is then slowly lifted at one end What is the maximum angle in units of degrees to the horizontal that the board can be at before the block begins to move The coefficient of static friction between the block and the board is 0 72 The coefficient of kinetic friction between the block and the board is 0 46

The coefficient of viscosity n of a liquid is defined as the tangential force on a layer in that liquid per unit area per unit velocity gradient across it Then a sphere of radius a moving through it under viscous force F attains a constant velocity v given by where K is a numerical constant 1 KF an 2 Kn 3 KE an 4 Kn

COA given object takes n times as much time to down a 45 rough incline as it takes to slide down a B perfectly smooth 45 incline The coefficient of kinetic friction between the object and the incline is given by 1 1 3 1 n 1 1 20 n 2 4 1 1 n 1 1 n N012

A box A is lying on the horizontal floor of the compartment of a train running along horizontal rails from left to right At time t the train decelerates Then the resultant contact force R by the floor on the box is given best by 1 2 3 4 R A floor A floor A floor A floor R

A rod supported on the wall starts slipping down If th speed VA of upper end A is 5 m s then the speed VB wit which end B will move to the left as shown in the figure is 1 5 m s 2 10 m s 3 5 3 m s 4 m s rod V B 60

One or more than one correct answer 19 A force F acts on the block so as to slide it on the rough horizontal floor It is impossible to push the block if is equal to friction coefficient between the block and the floor J m 90 D 0

A block of mass m is in contact with the cart C as shown in the figure C The coefficient of static friction between the block and the cart is The acceleration a of the cart that will prevent the block from falling satisfies 1 a mg 2 a 3 02 a Am 4 a 3 4 4 3c 12 A P a pa beac the lowe at re to t a equi bead wire 1 gh 2

8 On the horizontal surface of a truck u 0 6 a block c mass 1 kg is placed If the truck is accelerating at the rat of 5m sec then frictional force on the block will be 1 5 N 2 6 N 3 5 88 N 4 8 N

In the given figure the coefficient of friction between the two blocks is u and all other surface is smooth Find the minimum value ofF which will prevent slipping F 172 m 1 3 m m m g um m m g m 2 4 m m g um m m m g m

4 3g s 12 A piece of wire is bent in the shape of a parabola y kx y axis vertical with a bead of mass m on it The bead can slide on the wire without friction It stays at the lowest point of the parabola when the wire is at rest The wire is now accelerated parallel to the x axis with a constant acceleration a The distance of the new equilibrium position of the bead where the bead can stay at rest with respect to the wire from the y axis is 1 gk 2 3 2gk 2a gle

A vertical rectangular plane surface is submerged in water such that its top and bottom surfaces are 1 5 m and 6 0 m res pectively below the free surface The position of centre of pressure below the free surface will be at a distance of a 3 75 m 4 0 m b c 4 2m d 4 5m

2 29 A cubical block of mass 6 kg and side 16 1 cm is placed on frictionless horizontal surface It is hit by a cue at the top as to impart impulse in horizontal direction Minimum impulse imparted to topple the block must be greater than kg m s

A block of mass 10 kg is placed on an inclined plane When the angle of inclination is 30 the block just begins to slide down the plane The force of static friction is 1 10 kg wt 3 49 kg wt 2 89 kg wt 4 5 kg wt

A mass m hanging at the end of the string draws a mass m along the surface of a smooth table if the mass on the table be doubled the tension of string becomes 1 5 times then m m2 is m Question Type Single Correct Type 1 2 2 1 1 2 m

Consider following arrangement of three blocks A B and C Mass of the each block is 1 kg The coefficient of friction between any two blocks is 0 2 There is no friction between the block C and ground Find the minimum value of F in N for which sliding occurs at all the surfaces 8 A B C Smooth ground F

If the friction between the two blocks is 9N and ground is perfectly smooth then the maximum force which can be applied to the block of mass 2kg to present sliping is smooth 2 kg 3 kg f max

The coefficient of friction between the block A of mass m and wedge B of mass 2m is The inclined plane is smooth If the system of blocks A and B is released from rest and there is no slipping between A and B then the value s of 8 can be B A Fixed

Length AB in figure shown is 5 m The body is released from A friction is sufficient for pure rolling to take place The maximum time which rolling body can take to reach bottom is A 1 8 s C 30 2 2 s B

A marble block of mass 2 kg lying on long horizontal ice slab When given a velocity of 6 ms it is stopped by friction in 10 seconds Then the coefficient of friction is 1 0 02 2 0 03 3 0 06 4 0 01

What minimum force F is needed to start body A moving to the right if us 0 25 for all surfaces The following weights are given WA 125 N WB 50 N WAB 100 N The length of AB is 2 5 m Fig 5 10 Fig 5 60 1 6 m Z X

6 Block A has a mass of 2 kg and block B has 20 kg If the coefficient of kinetic friction between block B and the horizontal surface is 0 1 and B is accelerating towards the right with a 2 m s then the mass of the block C will be g 10 m s AC 1 15 kg 3 5 7 kg B C 2 12 5 kg 4 10 5 kg

2 20 A racing car moving towards a cliff sounds its horn The sound reflected from the cliff has a pitch one octave higher than the actual sound of the horn If V is the velocity of sound the velocity of the car is V V 1 2 2 2 V 3 m 4

Two masses m 10 kg and m 5 kg are connected by an ideal string as shown in the figure The coefficient of friction between m and the surface is 0 2 Assuming that the system is released from rest Calculate the velocity in m s when m has descended by 4m m m 4m

A body is sliding down a rough inclined plane which makes an angle 30 with the horizontal The co efficient of the friction between the surface of contact of the body and the plane is 0 5 Calculate the acceleration nearly m s O 0 7 0 2 5

One end of a heavy rod AB can slide along a rough fixed horizontal rod CD which it is attached by a ring B and C are bined by a string If ABC is right angle and a 37 be the angle between AB and vertical If rod AB with ring is in equilibrium hen minimum coefficient of friction between ring and horizontal rod is in the form lowest form Find b a D 90 8

It is found that on certain smooth inclined plane of angle 30 with horizontal a minimum force of 10 N is required to start a body up when applied parallel to inclined plane The minimum force required to be applied horizontally to start the same body up will be in N O 20 15 O 14

A block is placed on a rough plank moving with velocity 3 and velocity of block relative to plank is 31 4j find direction of kinetic friction force acting on the block 4 31 A C 31 i 10 31 4 5 B D 31 4 5 31 j 10

Max m SECTION 1 Answer all questions max marks 20 assume g 10 m s If required 1 A straight line represents uniform velocity acceleration in the distance time velocity time graph 2 2 The area under the V T graph represents for uniform acceleration motion only both uniform and non uniformly accelerated motion 2 3 A 20N force acts on moving body for 5s to bring it to rest What was the a initial momentum of the body and b the momentum 3s later 3 4 An opposing force of F acts on a mass M travelling with a velocity V How long does it take to stop the body Express your answer in terms of F M and V 2 5 What would be the acceleration of a body which is acted upon which is equal to half its weight 2 6 The gravitational force between two objects is 50 dynes when the separation between them is 1 2m What would be the force when the distance is increased to 6m 2 7 A vessel is filled to a level of 45 cm The pressure exerted on the wall at a point 20 cm from the base is 75 Pa What is the pressure X exerted on the floor 3 a force 20 cm 75 Pa Xw Pa 8 State one important reason for the atmospheric pressure to decrease drastically as we go up 1 9 The relative density of Mercury is 13 6 What is its density in Sl units 1 g cc 10 A body experiences an upthrust of 100gf when fully submerged in a liquid of density 1 25 What is the density of a liquid in which it experiences an upthrust of 150gf when fully 45 cm