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CBSE Questions for Class 8 Physics Friction Quiz 3 - MCQExams.com
CBSE
Class 8 Physics
Friction
Quiz 3
Friction opposes the _____ between two surfaces in contact.
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pressure
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current
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motion
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all of the above
Explanation
Frictional force acts against the applied force by opposing it and thus, obstructs the motion between the two surfaces.
Force that opposes the motion of any object even when no other external force is applied is called _____.
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electric current
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magnetic force
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frictional force
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mechanical force
Explanation
Frictional force always acts in direction opposite to that of the applied force. The irregularities between the two surface lock into each other, thus opposing any further motion even when no external force is applied to stop the moving body.
Arrange the level of difficulty of walking on the following surfaces in increasing order.
a) On wooden floor b) On concrete floor
c) On wet marble d) On dry marble
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c < b < a < d
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d < c < b < a
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b < a < d < c
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a < d < c < b
Explanation
Friction is created due to irregularities in the two surfaces in contact. We can walk on a floor when sufficient friction is present there. So, less friction, more difficult it is to walk and a higher chance of slipping. The irregularities on the concrete floor will be most followed by wooden floor, dry marble and wet marble. Thus, the most difficult surface to walk on will be wet marble followed by dry marble, wood and concrete.
Frictional force is more between which type of surfaces?
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Smooth
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Rough
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Both A and B
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None of the above
Explanation
Friction is caused due to the irregularities between two surfaces in contact. More the irregularities, the larger the roughness and more the friction between the two surfaces. Hence the frictional force is more between rough surfaces.
State whether the given statement is true or false :
Friction is necessary to perform many tasks.
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True
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False
Explanation
Friction helps to lock the two surfaces in contact.
However, if there was no friction, we would not be able to perform even simple tasks like writing on a paper, or fixing a nail in the wall, stopping or turning an automobile, or even something as simple as tying a lace knot. However, in some cases it is desirable to reduce friction but it can never be eliminated.
Which of the following factors affect friction ?
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Nature of the surface
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Weight of the object placed over other
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State of Motion of the object
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All of the above
Explanation
Friction force $$f=\mu N$$
Where,
$$\mu$$ is coefficient of friction. Its value depends on surface roughness or nature of surface, state of motion. If an object is in motion, Kinetic friction coefficient $$(\mu_k)$$ comes into use whereas when it is in rest then Static friction coefficient $$(\mu_s)$$ comes in use, and generally $$(\mu_s)>(\mu_k)$$.
$$N$$ is normal contact force, which depends on the weight of the object.
From the above discussion, we can say that Friction force depends on the nature of the surface,
Weight of the object placed over others,
State of Motion of the object.
Hence Option D
Can friction ever be eliminated?
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Yes
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No
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Sometimes
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Depends on the object in regard
Explanation
No matter how smooth or polished a surface might be, it will always have some irregularities at microscopic level. Thus, the friction can never be eliminated.
The substance that helps to ______ friction are called lubricants.
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increase
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decrease
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create
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eliminate
Explanation
Oils, grease, graphite, etc., are examples of lubricants. These form a thin layer between the two surfaces in contact thus avoiding them from scrubbing directly against each other. This makes the movement smooth and reduces friction.
Does the smoothness of a surface affect the frictional force?
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Yes
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No.
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Sometimes
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Can't say
Explanation
Friction is caused by the irregularities on the two surfaces in contact. Larger the irregularities, rougher is the surface and more the friction. Thus, the smoothness of the surface affects the frictional force.
Friction produces ______.
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light
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sound
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heat
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chemical
Explanation
Friction is produced due to the irregularities between surfaces. Thus, when these surfaces rub against each other they produce heat. And the heat gets trapped in these irregularities.
_______ helps in writing with a pen or pencil on a paper.
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Magnetic force
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Electric charge
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Chemical force
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Frictional force
Explanation
The irregularities between the paper and the pen or pencil create friction. Due to friction, the particles of ink or lead stick to the paper and get locked in its irregularities. If there would be no friction between the paper and pen or pencil, the ink/lead would not stick to the paper and we would not be able to write.
Friction is _____ in some situations.
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Desirable
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Undesirable
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Both A and B
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None of these
Explanation
Friction is both desirable and undesirable depending on the situation. For example, the tires of an automobile are grooved to increase friction. However, the ball bearings in the same automobile are regularly oiled to reduce friction and ensure the smooth functioning of the engine.
How do brake pads help in stopping an automobile?
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Brake pads press on the wheel and increase friction.
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Due to braking, the air pressure increases and the wheels stop.
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Both A and B
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None of the above
Explanation
The brake pads press on the wheels and increase the friction since the surface of the brake pads and the wheels are irregular, and the rough surface increases friction that opposes the motion of the wheel.
Kabaddi players rub their hands with soil so that they can :
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make their skin dry
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moisture the hands
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get a better grip while holding the opponent
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soil the opponent
Explanation
By rubbing their hands with soil, they make their hands rough. A rough surface has more friction which enhances their grip while holding the opponent.
Fluid friction depends on ______
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speed of the object
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shape of the object
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nature of fluid
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all of the above
Explanation
The speed of the object moving through a fluid affects the amount of friction acting against the motion of the object. More the speed, more is the friction. If the object is broad, it gives more area for the friction to act on. Thus, a streamlined body structure helps to cut through the fluid and reduce friction. Also, the nature of the fluid affects friction.
While the arrow moves towards its target, the force acting on it are due to gravity and due to ____ of air.
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gravitational force
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muscular force
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magnetic force
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frictional force
Explanation
When the arrow moves toward target, the force acting on it, is due to gravity and resistive force of air. The resistance force of air is also called as frictional force.
What is drag ?
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Frictional force offered by fluids
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Friction force offered by a solid surface
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Pulling a body over a surface
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None of these
Explanation
The other name for fluid friction is drag. It opposes the relative motion of any object in liquids or gases.
A ball rolling along the ground gradually slows down and finally comes to rest, which force is acting over here?
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force of friction
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magnetic force
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muscular force
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none of the above
Explanation
When a ball is rolling on ground ,there is a friction force which retards the motion of ball and makes it stop finally.Because friction always opposes relative motion between two surfaces.This friction force acts between two surfaces .Here this friction is between surface of ball and surface of ground.
Option A is correct.
Fluid friction is exerted by _____ .
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Solids and liquids
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Solids and gases
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Liquids and gases
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All the above
Explanation
Liquids and gases are together referred to as fluids and the frictional force exerted by them on various objects is called fluid friction.
In absence of friction
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our shoes will remain intact
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we will not be able to walk
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we will be able to slide smoothly
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all the above will happen
Explanation
Friction force always opposes relative motion between contact surfaces.
which results, we see wear and tear in machine parts or shoes.
But in absence of it, we will not be able to walk, our shoes will remain intact and we will be able to slide smoothly.
Hence Option D.
Fill in the blanks:
The________ force is the force exerted by a surface on an object when it moves across it or make an effort to move across it.
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Magnetic
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Friction
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Gravitational
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Electrostatic
Explanation
Frictional force acts between two surfaces to oppose the relative motion between the surfaces. It acts on the body moving across it or trying to move across it.
Fill in the blanks:
The force responsible for changing the state of motion of a moving object in contact between surface is the _______.
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non-contact force
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force of friction
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magnetic force
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muscular force
Explanation
The friction force is the force exerted by a surface an object moving across it. It acts in a direction to oppose the relative motion between objects.
Driving a car on a highway with windows open reduces the speed. This is due to:
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Air resistance
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Mechanical defect
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Bad driving
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None of these
Explanation
With windows open, air comes in and resists the motion of the car. So, due to air resistance, speed of the car reduces.
The taxi driver has to be more careful when driving car in winters because of morning dew. That means the friction on road during winter is _______ friction during summer. Fill in the blank.
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more than
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less than
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same as
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having no relation with
Explanation
A car moves forward due to friction and also can be controlled on road due to friction.
Due to the presence of dew, friction in winter is less than that in summer. Hence,
as the friction decreases, the possibility of car skidding increases. and the driver needs to be careful.
Which of the following affects friction?
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Nature of surface
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Temperature of surface
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Height of object
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Colour of surface
Explanation
Friction opposes the relative motion between two surfaces in contact. It acts on both surfaces. Friction depends on the nature of surfaces in contact. For a given pair of surfaces, friction depends upon the state of smoothness of those surfaces. Friction depends on how hard the two surfaces pressed together.
Fill in the blank.
Water offers _______ fluid friction as compared to honey.
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higher
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lower
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same
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zero
Explanation
Water, having less density than honey, offers lower fluid friction as compared to honey.
Which of the following statements is NOT true?
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Friction makes things slow down
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Friction produces heat
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Friction can stop moving objects
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Friction is not useful
Explanation
The statement that friction is not useful, is not true. Friction is advantageous in our daily life. Without friction, we will not be able to walk properly, nor drive vehicles even we can write anything on paper etc.
To move at the same speed, a car with a flat face and another with a streamlined body will require different amounts of force from the engine. The engine of the streamline bodied car will:
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Exert less force
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Exert more force
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Exert zero force
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None of these
Explanation
A car with streamlined body suffers less air friction while moving. And the car with a flat face will suffer higher air friction. As a result, the car with streamlined body will require less force from the engine to maintain the same speed.
The mover pushed his cart on tile floor and it went fast and easy. When he pushed his cart on carpet it was harder because there is more friction on carpet. What should he do to move his cart on carpet with equal speed?
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He should exert same force
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He should exert less force
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He should exert more force
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None of the above
Explanation
Carpet has a rough surface as compared to the tile floor, because of this friction is higher on the carpet as compared to the tile floor. As we know that friction is opposing force so the mover should increase the force to push the cart, when he is on carpet at the same speed.
________________ is a force that resists the movement of a solid object through a fluid.
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Thrust
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Magnetic force
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Fluid friction
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None of these
Explanation
By definition, fluid friction is a force that resists the movement of a solid object through a fluid.
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