Physics Class 9th Chapter 3 Questions and Answers :
In the study of physics, understanding the principles of dynamics plays a crucial role. Chapter 3 of the 9th-grade physics curriculum, titled "Dynamics," delves into the fascinating world of motion and explores various conceptual questions that arise from it. These questions aim to challenge students' critical thinking and analytical skills as they deepen their understanding of forces and motion. Covering topics such as inertia, friction, and Newton's laws of motion, this chapter equips students with the knowledge to analyze and explain the behavior of objects in motion. By providing answers to these conceptual questions, students can gain a comprehensive understanding of the fundamental principles and applications of dynamics, cultivating a solid foundation in the field of physics .This article will answers to all the conceptual questions of chapter 03 physic class 9th.
Question No 01
Why does dust fly off, when a hanging carpet is beaten with a stick?
Answer
Statement: Dust fly off when a hanging carpet is beaten with a stick.
Reason: When a hanging carpet is beaten with a stick, the dust particles are fly off because the carpet is set in motion while suddenly the dust particles are at rest due to inertia.
Therefore the dust particles get removed from the carpet.
Conclusion: Hence the dust fly off when a hanging carpet is beaten with a stick.
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Question No 02
If your hands are wet and no towel is handy, you can remove some of the excess water by shaking them. Why does this work?
Answer
Statement: if your hands are wet and no towel is handy, you can remove some of the excess water by shaking them.
Reason: The reason is that the excess water on our hands are at rest due to inertia while when we shake our hands the hands set in motion and the water remains at rest due to inertia.
Conclusion: Therefore the extra water is removed from our hands by shaking them .
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Question No 03
Why a balloon filled with air move forward when its air is released?
Answer
Statement: A balloon filled with air move forward when it's air is released.
Reason: According to the Newton's 3rd law of motion" every action has a reaction equal in magnitude but opposite in direction".
Air in the balloon is under pressure releasing that air out through the neck of the balloon produces action in the direction of air travels on exit .
Due to reaction of the action caused by the releasing of the pressurized air the balloon moves forward.
Conclusion: hence a balloon filled with air move forward when it's air is released.
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Question No 04
Why does a house pipe tend to move backward when the fireman direct a powerful stream of water towards fire?
Answer
Statement : A house pipe tend to move backward when the fireman direct a powerful stream of water towards fire.
Reason: according to Newton's third law of motion" every action has a reaction equal in magnitude but opposite in direction" .
When the fireman direct a powerful stream of water towards fire this produce action in the forward direction due to this action there is a reaction which move the pipe in the backward direction.
Conclusion: Hence the house pipe tend to move backward when the fireman directs a powerful stream of water towards fire due to the reaction of the action caused by the powerful stream of water in the pipeline.
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Question No 05
Your car is stuck in wet mud . Some students on their way to class see your predicament and help out by sitting on the trunk of your car to increase it's traction. Why does this help?
( Answer)
When a car stuck in wet mud, the friction between tyres and mud is
minimum as a result the car cannot come out of wet mud. The force of friction
is directly proportional to the normal force "FN i.e Fa F ( or) F fN.
when the students sit on the trunk of the car. The car the weight of the car
increases due to which the normal force "FN increases and the force of friction
also increases. Hence, the increase in friction helps the car to come out of the
wet mud easily.
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Question No 6
How does friction help you walk ? Is it kinetic or static friction?
Answer
Friction helps in walking:
Our ability to walk depends on friction between the soles of our shoes (or feet
and the ground. Since frictional force exists between soles of our shoes and the
ground. Thus due to this frictional force, we are able to walk on the ground
Without friction, it is not possible for us to walk on the ground.
The friction exists between the soles of our shoes and the ground is static frictionbecause the contact parts of our shoes are momentarily at rest with the ground.
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Question No 07
The parking brake on a car causes the rear wheels to lock up .what should be likely consequence of applying the parking brake in a car that in rapid motion?
Answer
Consequence of applying the parking brake in a car during rapid motion:
During rapid motion of the car, if the parking brake is applied the rear wheels
Mill be lock up while the front wheels are in motion. Due to inertia, the front
wheels try to maintain their motion. As the rear wheels are locked by applying
hand brake, so the car will skid in this case.
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Question No 08
Why is the surface of a conveyor belt made rough?
Answer
Statement: The surface of conveyor belt is made rough .
Reason: The surface of a conveyor belt is made rough to increase the friction between the object and belt .
Friction between object and belt does not allow the object to get a slip from the belt thus the things laying safe on the belt remains safe from falling down.
Conclusion:. Hence the surface of conveyor belt is made rough to increase the friction.
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Question No 9
Why does a boatman tie his boat to a pillar before allowing passengers to step on the river bank ?
Answer
Statement: A boatman tie his boat to a pillar before allowing passengers to step on the river bank .
Reason: According to Newton's third law of motion" every action has a reaction equal in magnitude but opposite in direction" .
When the passengers jumps from the boat and to step on river bank they applies force on the boat with their legs in the direction to that of motion.
As a result the boat moves backward and produce action.
For the reaction of that action the boatman tie his boat to a pillar before passengers to step on the river bank .
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Question No 10
Is velocity constant in uniform circular motion? Is acceleration constant in uniform circular motion? Explain.
Answer
velocity in uniform circular motion:
In circular motion the velocity does not remains constant. In circular
motion the direction of velocity changes continuously from point to point.
It is always tangent at that point. Thus the velocity does not remain constant during circular motion.
Acceleration in uniform circular motion:
The acceleration in circular motion (centripetal acceleration is directed towards the center of circular path i.e. its direction remain unchanged.
Thus uniform circular motion the centripetal acceleration remains constant throughout the motion.
Conclusion: Hence in uniform circular motion the Velocity changes continuously while the acceleration ( centripetal acceleration) remains constant throughout the motion.
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Question No 11
you tie a brick to the end of a rope and whirl the brick around you in a horizontal circle. Describe the path of the brick after you suddenly let go of the rope.
Answer
we tie a brick to the end of a rope and whirl it in a horizontal circle,
there are two forces acting on the brick
i. Centripetal force
ii. Centrifugal force
Centripetal force: we apply centripetal force to the brick through the rope.:
Centrifugal Force : The brick exerts centrifugal force on our hand through
the rope in a direction away from the center of the circle.
Path of the brick:
If we let go the rope suddenly, the brick moves away along the tangent
to the circle due to centrifugal force.
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Question No 12
Why is the posted speed for a turn is lower than the speed limit on most high ways?
Answer
Statement: The posted speed for a turn is lower than the speed limit on most of the high ways .
Reason: The reason is that when the speed is low the friction force is high so the body moving safely but when the speed is high the friction force is low and there are chances to turn out the body on the road.
Conclusion: hence the posted speed for a turn is lower than most of the high ways due to friction.
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