9th Class Chapter 5 Physics Short Questions

State and explain the law of universal Gravitation.

Law of universal Gravitation: Every in the universe attracts every other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

Why for some height larger and smaller satellites must have same orbital speeds?

The orbital speed depends upon the mass of earth and distance from the centr eof earth to the centre of mass of satellite and does not depend upon the mass of satellite. Therfore, for some particular distance from the centre of earth all the satellites have the same orbital speed irrespective of the size of satellite.

The value of 'g' changes with location on earth however we take the same value of 'g' as 9.8 ms-2 for ordinary calculations why?

The value of 'g' depends uponthe distance from the centre of earth. Greater the distance from the centreof earth, smaller will be the value of 'g' and vice versa. The change in the value of 'g' is significant only at very large distance. Therefore, we take same value of 'g' for ordinary calculation.

Moon is attractd by the earth, why it does not fall on earth?

The moon is natural satellite of the earth. It revolves around the earth in a specific orbit. The earth attracts the moon towards iteslf with gravitational forve. The gravitaational fore of earth provides necessarily centripetal force which compels the moon to move in the circular path. Beacuse of this orbital motion moon does not fall on earth.

Does the sun exert a larger force on the Earth than that exerted on the sun by the earth? Explain.

By Newton's third law the force exrted on the Sun by the Earth is exactly equal to the force the sun exrts on the Earth but in opposite direction.

If there is an attractive force between all objects, whey don't we feel ourselves gravitating toward nearby massive buildings.

Gravitational force pulls us to massive buildings but the forces are relatively smalldue to the small masses of us and buildings when compared to the mass of the earth. Therefore, the attractive force would be almost unnoticeable.

Why lighter and heavier objects fall at the same rate toward the earth?

Because value of 'g' does not depend upon the mass of the body, t depends only on mass of earth and radius of erth. There fore, lighter and heavier bodies fall towards earth with same acceleration.

How is the value of 'g' changing by going to higer altitude.

Variation of 'g' with altitude: The value of 'g' doesn\t depend upon the mas sof the body. It means that light and heavy bodie sshould fall towards the centre of earth with constant acceleration. However, the value of 'g' depends upon the distance of the body from the centre of the earth. Greater the distance from the centre of the earth, smaller will be the value of 'g' e earth That is why the value of 'g' at the poles is greater than at equator becasue earth is not a perfect square its equatorial radius is greater than the radius at the poles.

Derive the formula for the orbital speed of an artificial satellite.

Satellites: Satellites are the objects revolving around the planet in fixed orbits. Artificial satellites are man-made objets that revolve around the earth or other planets in different orbit with uniform speed due to gravitational force.A satellite requires a centripetal force to reolve around the earth and this necessary centripetal force is provided by the gravitational force of attraction betwene the earth and satellite.

Derive a formula to calculat ethe value of g.

Value of g: The Newton's law of Universal gravitation shows that value of g depends on mass of all reacting bodies and distance to it. So the value of 'g' can be determined by using law of gravitation.