14 State the action and reaction in the following:
(a) A swimmer swimming in a swimming pool
(b) Launching of a rocket
(c) Flight of a bird
15. State Newton's third law of motion. How will you
verify it experimentally?
16. State universal law of gravitation and express it
mathematically. What is the value of G?
17. State Newton's law of gravitation. What do you mean
by universal constant of gravitation G? What is SI unit
of G?
18. Briefly explain the importance of the law of
gravitation?
19. What is 'gravity'? Hence, define acceleration due to
gravity '&'. Is it a universal constant?
20. Using Newton's universal law of gravitation and
second law of motion, find the mathematical
expression for acceleration due to gravity on the
surface of the earth.
Answers
Answer:
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14.
(a) A swimmer while swimming in a swimming pool pushes his two hands simultaneously or one by one against the water behind himself. In which the force he applied by both the hands against the water pushes him forward against the water. So, force applied by the swimmer is the action here and the force which pushes him forward is the reaction here.
(b) A rocket exerts force below it because of the burning of its fuel which is the action here while the result which is movement of the rocket above the earth's surface is the reaction here.
(c) A bird flaps her wings up-down which pushes her upward and the force exerted by the two wings is adequate to let the bird fly and hence here the flapping of the bird is the action here while the bird still above the earth's surface is the reaction here.
15.
Newton's third law of motion states that every action has equal and opposite reaction. We can verify it experimentally by this:
Clap your both hands at the same time against each other with a certain force.
You will observe that when you clap harder against each other both palms get hurt it's because each palm exerts force against each other while there is also a reaction against each palm by the other one.
16.
Universal law of gravitation states that two bodies of mass m₁ and m₂ between a distance of d meters will exert gravitational force against each other, which is given by:
F = Gm₁m₂ / d²
Where, G = Gravitational constant
and G = 6.77 × 10⁻¹¹ N m² kg⁻²
Gravitational constant is the proportionality constant which is substituted in the equation to remove the proportionality and give us the actual magnitude.
17. Same as 16.
18.
Newton's law of gravitation applies for every large bodies in the universe. It is used for calculating the magnitude of force between planets and stars.
19.
Gravity is a force due to which two bodies of some mass attract each other.
Acceleration due to gravity ( g ) is the free falling acceleration that a body would experience when it's above the earth surface.
No, Acceleration due to gravity is not a universal constant because it depends upon the mass , radius, of the body.
20.
We know, Newton's law of gravitation,
F = Gm₁m₂ / d²
Let the mass of earth be M and distance between the body would be r because we have to find the value of g at the surface.
Since, the other body would exert negligible force against earth hence the mass of the body is also neglected from our calculation. So we are left with,
➞ F = GM / r²
Which is the rate at which the small body would be pulled towards the earth because there is no chance that the body would be pulling earth towards itself, hence,
➞ g = GM / r²