# Friction worksheet

Friction is defined as the force that opposes the motion due to the contact of the moving bodies.Here are the objectives question related to the friction to solve and analyze your knowledge  related to the friction.Answers are at the bottom of the worksheet.

1>The frictional force arises because of

(1) Interaction force between molecules of two bodies.

(2) Repulsive force between nuclei of two bodies.

(3) Gravitational force between two bodies

(4) Attraction between two nucleons.

2>Which of the following is maximum

(1) Static friction

(2) Limiting friction

(3) Kinetic friction

(4) Rolling friction

3>Which of the following is minimum

(1) Static friction

(2) Kinetic friction

(3) Rolling friction

(4) All are equal

4>Frictional force is

(1) Conservative

(2) Non-conservative

(3) Always constant in magnitude

(4) Always zero when a body is at rest

5>Frictional force is always proportional to

(1) Weight of body

(2) Normal reaction

(3) Area of surfaces in contact

(4) Absolute temperature

6>When a bicycle is in motion but not pedaled, the force of friction exerted by the ground on the two wheels is such that it acts

(1) In the backward direction on the front wheel and in the forward direction on the rear wheel

(2) In the forward direction on the front wheel but in the backward direction on the rear wheel

(3) In the forward direction on both the wheels

(4) In the backward direction on both the wheels

7>When a bicycle is in motion but pedalled, the force of friction exerted by the ground on the two wheels is such that it acts

(1) In the backward direction on the from wheel and in the forward direction on the rear wheel

(2) In the forward direction on the front wheel but in the backward direction on the rear wheel

(3) In the forward direction on both the wheels

(4) In the backward direction on both the wheels

8>Friction is

(1) Harmful in every case

(2) Useful in very case

(3) Harmful in some cases and useful in some cases

(4) Neither harmful nor useful

9>Which of the following statements about friction is true ?

(1) Friction can be reduced to zero

(2) Frictional force can accelerate a body

(3) Frictional force is proportional to area of contact between the surfaces

(4) Kinetic friction is always greater than a rolling friction.

10>Which one of the following is the self adjusting force.

(1) Static friction

(2) Limiting friction

(3) Kinetic friction

(4) Rolling friction

11>The angle between the frictional force and the instantaneous velocity of the body moving on the rough surface is

(1) zero

(2) $\dfrac{\pi}{2}$

(3) $\pi$

(4) $\tan ^{-1} ( \mu )$

12>A block of mass 2 kg is placed on the floor. The coefficient of static friction is 0.4. If a force of 2.8 N is applied on the block parallel to the floor, the force of friction between the block and the floor is

(1) 2.8 N

(2) 2 N

(3) 8 N

(4) zero

13>A block of mass 2 kg is placed on the floor .The coefficient of static friction is 0.4 and the coefficient of kinetic friction is 0.3. If a force of 12.8 N is applied on the block parallel to the floor is

(1) 12.8 N

(2) 2 N

(3) 6 N

(4) 8 N

14>In question (13) the acceleration of the block is

(1) 6.4 $m/s^2$

(2) 3 $m/s^2$

(3) 2.4 $m/s^2$

(4) 3.4 $m/s^2$

15>A particle placed on an inclined plane of slope angle 30° is just at the verge of sliding. The coefficient of static friction is

(1) $\dfrac{1}{2}$

(2) $\dfrac{1}{\sqrt{3}}$

(3) $\sqrt{3}$

(4) $\dfrac{1}{\sqrt{2}}$

16>A block has been placed on the inclined plane. The slope angle $\theta$ of the plane is such that the block slides down the plane at a constant speed. The coefficient of kinetic friction is equal to

(1) $\sin \theta$

(2) $\cos \theta$

(3) g

(4) $\tan \theta$

17>A body of mass 2 kg rests on a rough inclined plane making an angle of 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

(1) 9.8 N

(2) $0.7 \times 9.8 \times \sqrt{3}$ N

(3) $9.8 \sqrt{3}$ N

(4) $0.7 \times 9.8$ N

18>A block of mass 0.1 kg is held against a wall by applying a horizontal force of 5N on the block. If the coefficient of friction between the block and the mass is 0.5, the magnitude of the
frictional force acting on the block is

(1) 2.5 N

(2) 0.98 N

(3) 4.9 N

(4) 0.49 N

19>A mass M rests on a horizontal surface. The coefficients of friction between the mass and the surface is $\mu$. If the mass is pulled by a force F as shown in fig. ,the limiting friction between the mass and the surface is (1) $\mu Mg$

(2) $\mu [ Mg - \dfrac{\sqrt{3}}{2}Mg ]$ F

(3) $\mu [ Mg - \dfrac{F}{2} ]$

(4) $\mu [ Mg + \dfrac{F}{2} ]$

20>Pulling force making an angle 0 to the horizontal is applied on a block of weight W placed on a horizontal table. If the angle of friction $\phi$be the magnitude of the force required to move to body is equal to

(1) $\dfrac{W \cos \phi}{\cos ( \theta - \phi )}$

(2) $\dfrac{W \sin \phi}{\cos ( \theta - \phi )}$

(3) $\dfrac{W \tan \phi}{\sin ( \theta - \phi )}$

(4) $\dfrac{W \sin \theta}{g \tan( \theta - \phi )}$

21>Starting from rest a body slides from an 45 degree 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

22>A heavy uniform chain lies on a horizontal table top. If the coefficient of friction between the chain and the table surface is 0.25, then the maximum fraction of the length of the chain, that can hung over the one edge of the table is

(1) 20%

(2) 25%

(3) 35%

(4) 15%

23>The rear side of a truck is open and a box of mass 20 kg is placed on the truck 4 m away from the open end. The coefficient of friction between truck and box is 0.15 and g= 10 $m/s^2$. The truck starts from rest with an acceleration of 2 $m/s^2$ on a straight road. The box will fall off the truck when it is at a distance from the starting point, equal to

(1) 4 m

(2) 8 m

(3) 16 m

(4) 32 m

24>A particle is projected along a line of greatest slope up a rough plane inclined at an angle of 45° with the horizontal. If the coefficient of friction is $\dfrac{1}{2}$ , then retardation is

(1) $\dfrac{g}{\sqrt{2}}$

(2) $\dfrac{g}{2 \sqrt{2}}$

(3) $\dfrac{g}{\sqrt{2}} ( 1 + \dfrac{1}{2}$

(4) $\dfrac{g}{\sqrt{2}} ( 1 - \dfrac{1}{2}$

25>A block slides with a velocity of 10 m/s on a rough horizontal surface. It comes to rest after
covering a distance of 50 m. If g = 10 $m/s^2$, the coefficient of dynamic friction between the block and the surface is

(1) 0.1

(2) 0.2

(3) 0-5

(4) 1

26>A body of mass M is placed on the floor of a lift. If lift falls freely and the body is pulled horizontally, then the frictional force offered by the body is  ( $\mu^s$ = coefficient of static friction $\mu^k$ = coefficient of kinetic friction)

(1) $\mu^s Mg$

(2) $\mu^k Mg$

(3) $Mg$

(4) Zero

27>A block of mass 1 kg is at rest on a horizontal table. The coefficient of static friction between
the block and the table is 0.50 if g =10 $m/s^2$ ,  then the magnitude of the force acting upwards at an angle 60° from the horizontal that will just start the block moving is

(1)5 N

(2) 5.36 N

(3) 10 N

(4) 74.6 N

28>A 40 kg slab rests on a frictional floor. 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 coefficient of friction 0.40. The 10 kg block is acted upon by a horizontal force of 100 N. If g=9.8 $m/s^2$, the resulting acceleration of the slab will be

(1) 0.98 $m/s^2$

(2) 1.47 $m/s^2$

(3) 1.52 $m/s^2$

(4) 6.1 $m/s^2$

29>A string passing over a pulley contains 10 kg and 6 kg masses connected at its ends. The 6 kg mass hangs vertically, while 10 kg block is placed on the table. If the system is in dynamical equilibrium, i.e., moves with constant speed , the coefficient of dynamic friction is

(1) 0.3

(2) 0.6

(3) 0.10

(4) 1.67 30>Two masses A and B of 10 kg and 5 kg respectively are connected with a string passing over a frictionless pulley fixed at the corner of a table as shown in fig. The coefficient of friction of A with the table is 0.2. The minimum mass of C, that may be placed on A to prevent it from moving is equal to (1) 15 kg

(2) 10 kg

(3) 5 kg

(4) zero kg 