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CBSE Questions for Class 9 Physics Force And Laws Of Motion Quiz 7 - MCQExams.com
CBSE
Class 9 Physics
Force And Laws Of Motion
Quiz 7
Name the property of matter due to which a body continues to be in its state of rest or uniform motion unless an external force acts on it :
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Inertia
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Elasticity
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Viscosity
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Density
Explanation
Inertia is the tendency of any physical object to resist any change in its state of uniform motion or rest.
The resultant of balanced forces is :
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equal to infinity
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Equal to zero
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Not equal to zero
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Equal to the acceleration produced in the body
Explanation
Balanced forces cancel out the effect of each other resulting in a zero net force acting on the object.
Hence option B is correct.
Motion of a football after kicking is an example of:
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balanced force
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unbalanced force
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both A and B
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neither A nor B
Explanation
Kicking a football, being an unbalanced force, sets the ball into motion. Therefore, Option (B) is correct.
Force is _______.
Fill in the blank.
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a push
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a pull
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both A and B
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none of these
Explanation
Force is a push or pull which changes or tends to change the state of rest or of uniform motion.
The acceleration in a body is due to:
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Balanced force
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Unbalanced force
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Mass
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Temperature
Explanation
Unbalanced forces do not cancel out the effect of each other completely and thus resulting in a net external force acting in a particular direction causing the body to accelerate.
A force when applied on a non rigid object
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it does not change the inter spacing between its constituent particles
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it does not cause any change in its dimension
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it does not produce motion in it
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None
Explanation
A force when applied to a non-rigid object, the object can not hold its original shape. Therefore, the inter-spacing between the constituent particles changes. At the same time, the force causes a change in the state of motion of the object. So, none of the given options is correct.
Suppose a man is standing behind a stationary car. Which of the following options will be correct?
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The car will start moving towards the man
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The car will start moving away from the man
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The car will not move at all
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None of these
Explanation
The interaction of
one object with another object results in a
force between the two objects. If
a man is standing behind a stationary car,
there is no interaction between the man and the car, So no force act on the car, and hence the car does not move.
Mark the correct option.
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Mere presence of two objects brings force into action
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Interaction between two objects is necessary for bringing force into action
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Force is only a pulling force
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None
Explanation
$$Answer:-$$ B
Pushing, hitting and pulling of
objects
are all ways of
bringing objects
in motion.
This friction
force
arises
between two
surfaces in contact. No motion of the wood (in fig) will take place if it is at rest and equal forces in both direction are aplied, but no net
force
is
needed
to sustain the uniform motion of the marble.
By newtons third law:
For every action, there is an equal and opposite reaction. So two forces come into picturure for action.
Fill in the blank.
When a force is applied on a soft object,it changes the_________ of the object.
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Shape
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Size
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Direction of force
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Both a and b
Explanation
A soft object is a non-rigid object. Force can change the shape and size of a soft object.
When two equal forces act on an object in opposite directions, they are known as:
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Equivalent Forces
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Unbalanced Forces
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Balanced Forces
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Parallel Forces
Explanation
Balanced forces are equal and opposite in direction, they act on the same body. The net force due to these forces is zero.
Fill in the blank.
Interaction of one object with ________ results in a force.
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Itself
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Another object
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Both
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May itself and may be another object
Explanation
$$Answer:-$$ B
The best example we can take into account is the gravitational force.
Gravitation or gravity is a natural phenomenon
by which all things with mass
are brought toward
one another, including planets, stars,
and galaxies
.
A cricket ball hits and breaks a glass window and ends up inside the house. Identify which of the following statement is correct about the ball?
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The force the ball exerted on the window was larger than the force the window exerted on the ball
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The force the ball exerted on the window was smaller than the force the window exerted on the ball
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The force the ball exerted on the window was the same as the force the window exerted on the ball
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Since the ball broke the window, it didn't lose any momentum
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The kinetic energy the ball had before it broke the window equaled the kinetic energy the ball had after it broke the window
Explanation
According to Newton's third law, if a body exerts a force on another body, another body will exert an equal force on the first body. Therefore the force the ball exerts on the window is the same as the force the window exerts on the ball.
How does mitts help baseball players in catching the ball?
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The impulse delivered to the catchers hand is reduced due to the presence of the mitt
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The force on the catchers hand is reduced because of the increased area provided by the mitt
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The baseballs change in momentum is reduced due to the presence of the mitt
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The force on the catchers hand is reduced because the mitt increases the time of impact
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The force on the catchers hand is reduced because the mitt decreases the time of impact
Explanation
Mitts are made of multiple layers of leather and other soft materials. Multiples layers of Mitts increases the impact time of baseball in player hand which result Players experience less force on his hand while catching the ball.
Option D.
The force needed for something to change movement or change direction is known as:
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Balanced Force
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Equivalent Force
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Unbalanced Force
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Natural Force
Explanation
An unbalanced force acting on the object brings a change in the state and direction of the object. It is the cause of motion in the object.
A goldfish swims through an aquarium by moving its fins and tail. What causes the fish to move forward?
I. The force exerted by the water on the goldfish
II. The force exerted by the tail of the goldfish on the water
III. The force
exerted by
the fins of the goldfish on the water
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I only
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II only
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I and III only
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II and III only
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I, II, and III
Explanation
The fins and tail of goldfish exert force on the water in the backward direction and according to Newton's 3rd law of motion, the water exerts the same force on the goldfish in forward direction which helps it to swim in forward direction.
Which of the following is NOT an example of balanced force?
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Gravitaional force due to which table is steady on ground
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Two persons pushing box with same force in opposite direction
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See saw moving up and down
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None of the above
Explanation
'See saw' moving up and down is due to the unbalanced force, as it tilts down in one side, it means that force acting on that side is more and opposite side is less. An unbalanced force brings change in the state of motion or in state of rest of object,it is the cause of motion in object.
Box pushed from both direction with same force, so the net force is zero. Hence no movement is seen here. In other case table is also steady that means forces are balanced.
Inertia depends on which two factors:
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Height and Weight
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Length and Width
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Density and Mass
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Speed and Velocity
Explanation
Inertia depends on density and mass. Directly proportional to both of them.
The strength of force is expressed by?
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Direction
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Magnitude
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Both
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None
Explanation
Force could be larger or smaller than the other.the strength of a force is usually expressed by its magnitude.
When it is known that a net force is operating on an object, it is known that the object is:
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moving with constant velocity
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losing mass
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at rest
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being accelerated
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Gaining weight
Explanation
Second law of motion gives ,
$$F=ma$$ , where $$F$$ is force and $$m$$ is mass and $$a$$ is acceleration
given that net force is operating on object , as the mass of object remains constant therefore it is being accelerated.
And acceleration will be given by $$a=\dfrac{F}{m}$$
An arm wrestling competition among a strong person and a weak one is an example of?
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Balanced Forces
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Unbalanced Forces
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Net Force
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Frictional Force
Explanation
As both strong and weak person have different body weights and mass. A strong person can apply more force than a weak person. So this is an example of Unbalanced forces.
Which of the following type of forces is responsible for keeping a cart at rest or maintaining it moving at constant velocity?
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balanced forces
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gravity
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external forces
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friction
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unbalanced forces
Explanation
A balanced set of force is one where all forces cancel out each other to give a zero resultant force.
Such force would cause no acceleration and hence no change in velocity of object, and thus it would continue moving at constant velocity or it would be in rest.
A girl holds an orange at rest in her hand. One force in an action/reaction pair is the force of earth's gravity pulling down on the orange.
What is the other force in the action/reaction pair of forces?
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The force of the hand pushing up on the orange
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The force of the earth pushing up on the girl's feet
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The force of the orange pushing down on the girl's hand
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The force of the orange pulling up on the earth
Explanation
Sir Newton's third law states that for every action there is an equal and opposite reaction, action and reaction act on different objects.
When weight of orange (gravitational pull) acts on the hand vertically downward, the normal force on orange by hand acts pushing the orange upward.
Which of the following best describe about the statement " An object slides on a horizontal, frictionless surface".
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Inertia
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Unbalanced forces
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Action and reaction force pairs
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Universal gravitation
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Simple harmonic motion
Explanation
Law of inertia states that present state (in motion or stationary) of a body does not change until an external force is applied on it .
As the object slides on a frictionless surface it means no external force is working on it ,so body will continue to slide due to inertia of motion.
A book rests on a table, exerting a downward force on the table. The reaction to this force is
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the force of Earth on the book
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the normal force acting on the book because of the table
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the force of Earth on the table
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the inertia of the book
Explanation
The reaction is always in opposite direction to the action and action and reaction always act on different bodies , according to Sir Newton's third law .Hence , reaction to the action of book on table will be the force of the table on the book .
A ball falls freely towards the Earth. If the action force is the Earth pulling down on the ball, then identify which of the following best describe the reaction force:
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the ball pulling up on the Earth
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air resistance acting on the ball.
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the ball striking the Earth when it lands.
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the inertia of the ball
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there is no reaction force in this case.
Explanation
The earth is pulling the ball down during its motion.
According to Newton's 3rd law of motion, every action has equal and opposite reaction.
Thus the ball is also pulling the earth in the upward direction.
Which one of the following is equal to $$1$$ Newton?
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$$1\ kg\cdot m^{2}/s$$
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$$1\ kg\cdot m/s^{2}$$
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$$1\ kg^{2} / s$$
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$$1\ kg^{2}\cdot m/s$$
Explanation
Force acting on a body $$F = mg$$ Newton
$$\therefore$$ $$1$$ Newton $$ = 1$$ $$kg.m/s^2$$
A force of a given magnitude acts on a body. On what factors does the acceleration of the body depend?
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Density of the body
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Volume of the body
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Mass of the body
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Shape of the body
Explanation
$$F=ma$$
when F is constant
$$a\propto \dfrac{1}{m}$$
What would happen to a car traveling west at a constant velocity of 55 MPH without any influence of external force?
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The car would continue moving west with a velocity of 55 MPH
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The car would slowly increase its velocity approaching but not reaching the speed of light
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The car would slow down but never reach 0 velocity
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The car would slow down and come to rest
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The car would increase its velocity without changing acceleration
Explanation
With no external force acting on the car, the state of motion of the car would not change. Therefore, the car would continue to move with the same velocity, i.e. $$55\ MPH$$ towards the west.
A physics book rests on a table top. A gravitational force pulls down on the book. According to Newton's third law. The force that is equal to this gravitational force is:
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the force the table exerts upward on the book.
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the force the book exerts downward on the table.
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the force the table exerts downward on the table.
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the force the book exerts upward on the table.
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the force the air pressure exerts down on the book.
Explanation
Sir Newton's third law of motion states that for an action there is always an equal and opposite reaction . These two forces always act on different objects . When a book is kept on a table , weight (gravitational force) of book acts on table vertically downwards and as a reaction of weight , table also exerts an equal and opposite ( upward) force on book .
Consider a porter standing on a platform with a suitcase which presses his head with a force of 200 N. If this force is taken to be the action, from where is the reaction force exerted and to where is it directed ?
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The head, on the suitcase
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The earth, on the suitcase
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The earth, on the porter
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The suitcase, on the earth
Explanation
According to Newton third law reaction force of 200N will be opposite to the direction of action and is upwards and caused by the porter from his head.
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