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CBSE Questions for Class 8 Physics Force And Pressure Quiz 4 - MCQExams.com
CBSE
Class 8 Physics
Force And Pressure
Quiz 4
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
Fill in the blank.
____ exert pressure on the walls of the containers.
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Only gases
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Only liquids
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Gases and liquids
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Neither gases nor liquids
Explanation
Gases and liquids, in a word, fluids exert pressure on the walls of the containers.
Under action of which force does water flow from an open tap towards ground?
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Electrostatic force
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Magnetic force
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Gravitational force
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None of the above
Explanation
Objects tend to move downwards to the earth because of gravity of the earth. This force, exerted on the object is known as force of gravity.
The force of gravity acts on all objects. The force of gravity acts on all of us all the time without our being aware of it. Water begins to flow towards the ground as soon as we open a tap because of gravitational attraction by earth. Water in rivers flows downward due to the force of gravity.
Does moon have its own gravity?
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No
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Yes
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Not known yet
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Only during full moon
Explanation
Gravity is not a property of the earth alone. Every object in the universe exerts a force on every other object. This is called gravitational force. Naturally, the moon also has its own gravity.
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.
What is muscular force?
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Force due to gravity
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Force due to charges
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Force resulting due to action of muscles
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Force resulting due to rubbing
Explanation
Force resulting due to action of muscles is known as muscular force.
For example, lifting, getting up from a seat, crossing a leg, etc.
When a ball is hit by a bat, forces acting on the ball are
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muscular force
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gravitational force
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both A and B
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neither A nor B
Explanation
Being hit by a bat, muscular force acts on the ball through the bat. And, it is also in gravitational field so traditional force also act on It. So, the forces acted upon the boll are both muscular and gravitational force.
When you ride a cycle, force(s) acting on the cycle is/are
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muscular force
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force of friction
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gravitational force
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all of the above
Explanation
To ride a cycle, you have to apply muscular force on the pedals of the cycle. The tyres of the moving cycle are acted upon by the force of friction of the road. And, all objects on the earth are acted upon by the gravitational force towards the centre of the earth.
Which of the following is not an example of muscular force?
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An animal pulling a cart.
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A man pushing a stationary car.
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An apple falling from a tree.
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Two girls pushing each other.
Explanation
An apple falling from a tree is an example of gravitational force.
An animal pulling a cart, a man pushing a stationary car and two girls pushing each other are examples of muscular force because f
orce
which is exerted by
muscles
of the body is called
Muscular force
.
Which of the following is an example of muscular force?
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Two magnets attracting each other.
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An apple falling from a tree.
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Charges produced by friction.
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None of these
Explanation
Two magnets attracting is an example of magnetic force.
An apple falling from a tree is an example of gravitational force.
The charge produced by friction is an example of frictional force.
In tug of war, if the two teams have equal strength then:
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The rope will break.
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The rope will stay at the same place.
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The rope will move towards one of the sides.
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The rope will move towards each end alternatively.
Explanation
The rope breaks only if the force applied by both the teams is very large. It has nothing to do with the equality of the strength in the teams on the two sides of the rope.
In a tug of war, if the two teams are applying equal force on the rope then the net force acting on the rope is zero and hence the rope stays at the same place.
Which of the following is a non-contact force?
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Gravitational force
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Magnetic forces
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Electric force
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All
Explanation
It is not necessary for the two objects to be in contact (touch) with each other to exert gravitation force, magnetic force and electric force. These three forces can be exerted even if the two objects are separated by a finite distance. Thus these forces are non-contact forces.
If the forces on an object are balanced, then the net force is:
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Either positive or negative depending on the strength of forces.
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Negative
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Positive
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Zero
Explanation
If the forces on the object are balanced, this means that the individual force cancel out each other resulting in a zero net force acting on the object.
Mark the correct statement(s).
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Forces in the same direction combine by addition.
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Forces in opposite directions combine by subtraction.
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Forces in the same direction combine by subtraction.
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Forces in opposite directions combine by addition.
Explanation
Resultant of two forces in same direction is found by addition whereas resultant of two forces in opposite direction is found by subtraction.
A number of forces act on a body at the same point and the body does not move. What do you conclude from this?
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Body is acted upon by a set of balanced forces.
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Body is acted upon by a set of unbalanced forces.
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Body is acted upon by a set of unknown forces.
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None of the above
Explanation
Balanced forces cancel out the effect of each other. Thus, no net external force acts on the body and hence a body at rest does not move.
In a tug of war, there are two teams - A and B. A applies $$200\ N$$ force and B applies $$1000\ N$$ force in the opposite direction. Choose the correct statement(s).
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The rope will stay at the same place.
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The rope will break.
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Rope will be drawn towards A.
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Rope will be drawn towards B.
Explanation
Force applied by team A: $$F_A = 200\ N$$ (towards A)
Force applied by team B: $$F_B = 1000\ N$$ (towards B)
Net force, $$F_{net} = F_B-F_A = 1000-200 =800\ N$$ (towards B)
So, the force applied by team-B is more and hence the rope will be drawn towards B.
Magnetic force is a non contact force because, for magnetic force to apply,
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The bodies have to be in contact.
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The bodies need not be in contact.
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The bodies may or may not be in contact.
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None of these.
Explanation
Magnetic force, electric force and gravitational forces are non contact forces because for these forces to apply, the bodies need not be in contact (physically touch) with each other.
Which of the following is not a contact force?
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Tension force
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Normal force
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Air resistance
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None
Explanation
Tension force applied by a rope on a body needs physical contact to pull the body.
Normal force acts between two surfaces in contact. If two surfaces are not in contact, they can't exert a normal force on each other.
Air resistance is the force
in opposition to the relative motion of an object as it passes through the air. Here also, the air particles in contact with the surface of the object rub against it to slow it down.
All these forces are called as contact forces.
Hence, option D is correct.
A set of unequal and opposite forces is called:
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Balanced forces
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Unbalanced forces
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Equilibrium forces
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None
Explanation
Unequal and opposite forces do not cancel out each other completely and thus resulting in net force acting in a particular direction. A set of such forces is called a set of unbalanced forces.
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.
When a football is kicked, its shape changes for a fraction of a second. This is because
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force changes the shape of an object
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force does not change the shape of an object
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momentum changes the shape of an object
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motion changes the shape of an object
Explanation
Football is deformable body When a football is kicked, a contact force is applied and thus its shape changes. Hence
Force
is responsible to
change its shape.
Other than changing the state of motion of an object, force
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can change the shape of an object
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has no other effect
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can change the colour of an object
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can change the state of rest of an object
Explanation
Effects of force on an object are
(i) to change the state of uniform motion and rest of the object
(ii) to change the shape and size of the object
Hence Option A and D are correct
You are pushing a ball. If your younger sister pushes it from the opposite side with lesser force, the ball will
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move slower
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move faster
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move at same speed
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move in another direction
Explanation
When forces are applied from opposite directions, the forces get subtracted. So, the resultant or net force is less than the force which was applied initially. As a result, the object's speed will reduce.
Here, if you are pushing the ball with force $$F_1$$, and your sister is pushing it with force $$F_2$$ then the net force will be
$$F_{net}=F_1-F_2$$
Since $$F_1>F_2$$, then the net force $$F_{net}$$ is obviously less than $$F_1$$ which you were applying., and hence the ball moves slower.
You alone can push a roller. But when your friend joins you, the roller moves faster. This is because:
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forces in same direction add up.
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forces in same direction do not add up.
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forces in same direction get subtracted.
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forces in same direction remain same.
Explanation
When your friend joins you, both of you push the roller in same direction. So, your forces, being applied in same direction, add up to a larger value. Thus the roller moves faster.
To pull a heavy goods' train, two engines are often connected one after another. This is to
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increase the pull
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decrease the pull
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save the power
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do none of these
Explanation
Since both engines will try to pull in the same direction so their pull forces will add up and total pull on the train will increase which will make it easier to pull it.
A spring is compressed when a force is applied. This is an example of
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force changing the shape of an object
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force changing the motion of an object
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force breaking a rigid object
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none of these
Explanation
A spring gets compressed by the application of a force. This is an example of one of the effects of force: that it can change the shape of an object.
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.
If a force changes the shape of a body, the body should be
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non-rigid
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rigid
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fluid only
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none of these
Explanation
An object that is easily folded on application of force and has a lot of flexibility is called a non-rigid body.
When a force is applied on a non-rigid body, its shape changes.
When a force is applied on a non-rigid object,
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its shape changes
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its shape remains same
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only its state of motion changes
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nothing happens
Explanation
A non-rigid body can not hold its shape when a force acts on it. It deforms under the action of the force. So, force can change the shape of a non-rigid body.
When a spring is pulled:
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Shape of the spring changes
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Size of the spring changes
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Size of the spring doesn't change
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Both $$A$$ and $$B$$
Explanation
Force is an external agent (push or pull) which changes the state of motion or rest of an object.
When spring is pulled, both the
shape and
size of the spring change.
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