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CBSE Questions for Class 9 Physics Force And Laws Of Motion Quiz 6 - MCQExams.com
CBSE
Class 9 Physics
Force And Laws Of Motion
Quiz 6
Internal forces
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Are always balanced
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Are never balanced
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May or may not be balanced
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None of these
Explanation
Internal Forces are forces between objects found inside the system. They are always balanced or their vector sum is always zero and cannot do work on the system.
A body can change its state of rest or of uniform motion on its own. True or false.
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True
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False
Explanation
Newton's first law of motion states that a body can change its state of rest or of uniform motion only
when acted upon by some external force.
Fill in the blanks:
A push or a pull on an object are types of ________.
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pressure
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attraction
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repulsion
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force
Explanation
Force is required to move a stationary object, to stop a moving object, etc. The phenomenon required to push or to pull on object is force.
Identify the action involved when a magnet attracts a piece of iron towards it.
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Pushing
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Pulling
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Flying
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Picking
Explanation
When a magnet is placed near to the pieces of iron, it pulls the pieces of iron towards itself due to it's magnetic field action . So the action involved is pulling.
Identify the action involved in opening or shutting a door.
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Pulling
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Pushing
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Both a and b
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None of the above
Explanation
We need to apply a PULL when trying to open a door.
We need to apply a PUSH when trying to close a door.
Which of the following actions can be grouped as push?
a. A cricket ball hit by a batsman.
b. A football player kicking the ball.
c. A girl is shutting the open door of a refrigerator.
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Only a
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Only a and b
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only b and c
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a, b and c
Explanation
All the above examples can be grouped as push. As the force is applied to move the object away.
In which of the following cases, a force is not being applied?
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A man standing behind a stationary car.
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A car being pushed by a man.
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A man trying to stop a sliding car.
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A man standing on a car.
Explanation
For pushing a car, a force is required in the direction of motion of the car.
In trying to stop a sliding car, a force is required against the direction of motion of the car.
A man standing on the car applies the force of weight on the car.
But, to stand behind a stationary car, no net force needs to be applied on the car.
Option A
Which of the following actions can be grouped as pull:
a. Moving a loaded cart
b. Applying brakes while driving car
c. Drawing a bucket of water from a well
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Only a
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a and b
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b and c
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a and c
Explanation
For moving a loaded cart and drawing a bucket of water from a well, the action involved is pulling hence can be grouped as Pull.
What happens when there is no interaction between the objects?
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Force comes in action.
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Force does not come in action.
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Force may or may not come in action.
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None of the above is correct
Explanation
There are two types of force
1) Interactive force: Its effect comes when two objects will come in contact.
2) Non- Interactive force: Its effect will come when an object comes in their respective field strength.
exp: Charge in an electric field, Mass in gravitation field.
Hence Option C.
Group the following examples as a pull or a push or both?
(i) Opening a drawer
(ii) Opening or shutting a door
(iii) Hitting a ball
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Pull - (i)
Push and Pull - (ii)
Push (iii)
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Pull - (ii)
Push and Pull - None
Push (i & iii)
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All are examples of pushing
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All are examples of pulling
Explanation
To open a drawer action involved is pull, for opening and shutting a door both action is involved, hitting a ball pushing involved.
A force acts between two bodies if:
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both the bodies are pushing each other.
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both the bodies are pulling each other.
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either of the two bodies are pushing or pulling the other body.
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all of these
Explanation
Force is kind of a push or a pull. So, in all the above cases there is a force acting between two bodies.
Fill in the blanks:
In the game of tug-of-war, both the teams pulls each other. So ________.
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force is applied due to interaction.
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force is not applied although there is interaction.
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force is applied although there is an interaction.
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none of the above.
Explanation
Force always comes into action when there will be interaction between the objects, Here both the teams are exerting force on each other through the rope.
Fill in the blanks:
An interaction of one object with another object results in a _________ between the two objects.
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Pressure
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Attraction
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Force
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Repulsion
Explanation
When one object interacts with another object they exert force on each other, either towards or away from each other.
Fill in the blanks:
Force comes into action when ________.
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objects interact.
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objects do not interact.
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object move.
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None of these
Explanation
When two body interact with each other then momentum of body will change that change in momentum of the body is effect of mutual force between them.
In which direction does a car at rest move when pushed by a few persons?
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In the direction
opposite to
push
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In the direction of the push
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Making an acute angle with the push
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None of the above
Explanation
To move a car there must be interactions between the men and the car. The interaction is exerted in terms of push and the car moves in the direction of net force which is the direction of push, i.e., in the direction of the force applied.
Mark the correct statement(s).
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When unbalanced forces act on an object at rest, the object will move.
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Unbalanced forces are necessary to cause a non-moving object to start moving.
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Unbalanced forces produces change in motion (acceleration).
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All
Explanation
Unbalanced forces result in a non-zero net external force acting on a body which produces an acceleration of the body in a particular direction and hence the body at rest starts to move in that direction. Thus unbalanced forces are necessary to cause a non moving object to start moving. Thus option D is correct.
The force acting on an object are balanced, then the object:
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must be at rest
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must be moving
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must not be accelerating
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must lose energy
Explanation
Balanced forces always result in a zero external force acting on an object i.e $$F_{ext} =0$$
$$\therefore$$ Acceleration $$a = \dfrac{F_{ext}}{m} = 0$$
Thus the object must not be accelerating or it must be moving with constant velocity or remain at rest (if it was at rest initially). Hence option C is correct.
______ of the body is a measure of inertia. Fill in the blanks.
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Mass
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Force
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Velocity
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Speed
Explanation
The object having the greatest mass has the greatest inertia. Thus mass is the measure of inertia.
Inertia is __________.
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A property of mass
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A type of force
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The speed of an object
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None of these
Explanation
The mass of an object is a measure of its inertia. Its SI unit is $$kilogram\ (kg)$$.
When you hit a wall and sponge with equal force. Which case will hurt more?
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Both equally
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Wall
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Sponge
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No comparison
Explanation
When you apply force (hit) on a wall, the wall too applies equal and opposite force on your hand. The wall applies a huge force on your hand and takes a very short time to stop the impact. Lesser the time taken to stop the impact, more is the impulse on your hand. So, you get more hurt.
Whereas, when you hit a sponge, your hand goes inside the sponge to some extent, due to which more time is required to stop the impact. So, the impulse on your hand is comparatively less, due to which you are less hurt when you hit a sponge.
Hence,
Option B
What kind of force is required to accelerate the motion of an object?
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Balanced force
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Unbalanced force
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Pressurized force
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Equal and opposite force
Explanation
Unbalanced forces produce a resultant force acting on the object in a particular direction which tends the object to accelerate in that particular direction.
Which is correct for balanced and unbalanced forces?
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If set of forces acting on body results in change in state such forces are called unbalanced forces
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Object is in equilibrium if sum of all forces is zero i.e. $$\sum F_x = 0$$
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The object is in non-equilibrium state and the resultant force is non-zero. i.e. $$\sum F_x \neq 0$$
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All
Explanation
If a set of forces acting on a body does not change the state of rest or of motion of an object such forces are called balanced forces. In this case object is said to be in equilibrium state. The vector sum of all forces is zero i.e. $$\sum F_x = 0$$.
Set of forces acting on body results in change in state i.e. either changes the speed or direction, such forces are called unbalanced forces. In this case the object is in non-equilibrium state and the resultant force is non-zero. i.e. $$\sum F_x \neq 0$$.
A batsmen hits a sweep short in the game of cricket. What is the nature of force experienced by the ball during the impact?
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Balanced force
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Unbalanced force
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Both Balanced and Unbalanced forces
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Neither balanced not unbalanced force
Explanation
We know that balanced forces mean that these forces will not produce net momentum to the body.But unbalanced forces provide net momentum to the object.
During impact, the direction of the ball and its speed changes. Hence, momentum changes. Thus, an unbalanced force is applied on the ball.
Spring scale reads $$20\ N$$ as it pulls a $$4.0\ kg$$ object across a table. What is the magnitude of the force exerted by an object on the spring scale?
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$$40\ N$$
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$$20\ N$$
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$$4\ N$$
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$$5\ N$$
Explanation
According to Newton's third law of motion, every action has its equal and opposite reaction.
Thus the object exerts the same amount of force on the spring scale as the force exerted by the spring scale on the object i.e. $$20$$ $$N$$.
"Every action has its equal and opposite reaction" is Newton's:
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First law of motion
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Second law of motion
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Third law of motion
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Fourth law of motion
Explanation
Newton's third law of motion states that every action has an equal and opposite reaction. Force on a body 2 applied by the body 1 $$(F_{21})$$ is equal and opposite to the force on body 1 applied by the body 2 $$(F_{12})$$, i.e.
$$F_{21}=-F_{12}$$
If two bodies do not interact
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still a force can be applied
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no force can be applied
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contact force can be applied
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non-contact force can be applied
Explanation
If two bodies do not interact there won't be any force between them as
interaction is must for having any sort of force between two bodies.
The law that gives a qualitative definition of force is :
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Newton's second law of motion
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Law of inertia
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Newton's third law of motion
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Law of gravitation
Explanation
Law of inertia states that the body tends to remain in the same state (regarding its velocity and direction) untill no external force is acting on it.
Hence option B is correct.
Catching a cricket ball 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
Catching a cricket ball, being an unbalanced force, causes the change in state of motion of the ball.
In order to apply a force on the body:
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there has to be an interaction.
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there must be no interaction.
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sometimes there may be an interaction.
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None of these
Explanation
Two bodies must interact in order to apply a force.
Whenever we see a force acting we see actually two bodies exerting force on each other. As per third law forces apply in pairs always.
So actually whenever we note a force there are actually two forces and two bodies interacting mutually.
An unbalanced force:
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never tends to change the state of motion of the body
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tends to change the state of motion of the body
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never exists
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does not provide acceleration to a body
Explanation
An unbalanced force tends to change the state of rest or of uniform motion of the body. This force provides acceleration or retardation to the body.
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