9th Physics Chapter 3 Dynamics Short questions
9th Physics Chapter 3 Dynamics Short questions answers will be solved.
Q1 What kind of changes in motion may be produced by a force ?
Force can change the speed, direction, shape, size and state of an object.
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Q2 Give 5 examples of contact forces.
A force that is exerted by one object on the other at the point of contact is called contact force.
Examples of contact forces are friction, thrust, air resistance, drag force, normal force, tension force and elastic force.
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Q3 An object moves with a constant velocity in free space. How long will the object continue to move with this velocity ?
Due to Newton’s first law of motion the object will move forever unless the object experiences an external force.
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Q4 Define impulse of force ?
Impulse is the total change in momentum of an object.
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Q5 Why has not Newton’s first law been proved on the Earth ?
There is no proof of Newton’s first law on Earth. Because according to science, Earth is continuously rotating about the sun and spinning about its own axis.
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Q6 When sitting in a car which suddenly accelerates from rest, you are pushed back into the seat, why ?
It happens due to inertia. Body is initially at rest. When car suddenly accelerates, body resists due to inertia but seats pushes you forward. As a result, seat pushes you back.
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Q7 The force expressed in Newton’s second law is a net force. Why is it so ?
An object can experience many forces. These forces can combine or cancel each other. The net force is the sum of all the forces. Hence only net force can the change the motion.
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Q8 How can you show that rolling friction is lesser than the sliding friction ?
Sliding friction occurs due to direct contact of the surfaces but there is less direct contact of the surfaces in rolling friction. Hence, rolling friction requires less friction than sliding friction. We can experience it by sliding a book on the table and rolling a book on set of pencils.
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Q9 Define terminal velocity of an object.
Terminal velocity is the constant maximum velocity of a freely falling object when the force of gravity is balanced by the air resistance and no further acceleration occurs.
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Q10 An astronaut walking in space wants to return to his spaceship by firing a hand rocket. In what direction does he fire the rocket ?
Astronaut will fire the rocket opposite to the direction of spaceship. As an action, he will fire the rocket and as a reaction he will go back towards the spaceship.
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