Gravitation

Q 1.

State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?

Q 2.

Calculate the force of gravitation between the Earth and the Sun,given that the mass of the Earth = $6x1024$ kg and mass of the Sun = $2\; x\; 1030$ kg. The average distance between the two is $1.5x1011$ m.

Q 3.

Can you calculate density of Earth from Newton’s law of gravitation ?

Q 4.

What do we call the gravitational force between the Earth and an object ?

Q 5.

What is the value of ‘g’ at the centre of Earth ?

Q 6.

What do you mean by acceleration due to gravity ?

Q 7.

At what height above the surface of the earth, the value of 'g' becomes 64% of its value at the surface of the earth. Take radius of the earth = 6400 km.

Q 8.

Why do sewing needles and all pins have a sharp pointed tip?

Q 9.

A particle is dropped from a tower 180 m high.How long does it take to reach the ground ? What is the velocity when it touches the ground ? Take g = $10\; m/s2$

Q 10.

Suppose a planet exists whose mass and radius both,are half those of Earth.Calculate the acceleration due to gravity on the surface of this planet.

Q 11.

Fill in the blanks :
Weight of an object is the product of ______ and ________.

Q 12.

Fill in the blanks :
Every object in the universe ________ other bodies.

Q 13.

Two stones A and B are dropped from a multistoried building. A is dropped from 100 m and after some time B is dropped from 50 m height. Both of them reach the earth at the same time. Will they have equal velocity while reaching the ground ? Calculate and find out the answer (take g =10 m/s²).

Q 14.

Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 × 10²⁴ kg and of the Sun = 2 × 10³⁰ kg. The average distance between the two is 1.5 × 10¹¹ m.

Q 15.

Is weight a scalar quantity?

Q 16.

Calculate the value of acceleration due to gravity on Moon. Given mass of Moon = $7.4x1022$ kg, radius of Moon = 1740 km

Q 17.

Fill in the blanks :
________ of an object is the force of gravity acting on it.

Q 18.

A boy on a clif£ 49 m high drops a stone.One second later,he throws a second stone after the first.They both hit the ground at the same time. With what speed did he throw the second stone ?

Q 19.

In Fig.,the line that joins a planet to the sun sweeps out areas $A$₁$A$₂,$A$₃in time intervals 6 weeks,3 weeks and 2 weeks respectively.How are $A$₁ $A$₂,$A$₃ realted ?

Q 20.

Mass of an object is 10 kg. What is its weight on the Earth? (g = 9.8 m/s².)

Q 21.

Fill in the blanks :
The SI unit of mass is ______.

Q 22.

Fill in the blanks :
The gravitational force between the earth and the object is generally called ____________.

Q 23.

Why does an object float or sink when placed on the surface of the water?

Q 24.

The mass of Earth is $6x1024$ kg and that of moon is $7.4x1022$ kg. If the distance between the Earth and the Moon is $3.84x105$ km, calculate the force exerted by Earth on the Moon. Given G = $6.7x10-11$ $Nm2/kg2$.

Q 25.

What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?

Q 26.

How does the force of gravitation between two objects change when the distance between them is reduced to half ?

Q 27.

The distance between two objects is doubled. What happens to gravitational force between them

Q 28.

A stone falling towards Earth also attracts the Earth with the same force.Is it true ?

Q 29.

On earth,value of G = $6.67x10-11N\; m2K\; g-2$.What is its value on moon,where g is nearly $\frac{1}{6}$th that of earth ?

Q 30.

Fill in the blanks :
Heliocentric model was proposed by ______.

Q 31.

Fill in the blanks :
The value of g on the earth's surface is ______.

Q 32.

Fill in the blanks :
The value of g ________ (increases/decreases) as we go upwards from the earth's surface.

Q 33.

What was heliocentric theory? Who proposed this?

Q 34.

How is gravitational force of attraction between two bodies affected if(i) Mass of both bodies is doubled.(ii) Distance between them is halved.

Q 35.

Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?

Q 36.

Define weight? How it is related to mass?

Q 37.

A stone is allowed to fall from the top of a tower 100 m high and at the same time another stone is projected vertically upwards from the ground with a velocity of 25 m/s. Calculate when and where the two stones will meet.

Q 38.

Define thrust.

Q 39.

Is mass a scalar quantity?

Q 40.

Define gravity.

Q 41.

What are the factors the buoyant force depends on?

Q 42.

What are Plimsoll Lines?

Q 43.

Why will a sheet of paper fall slower than one that is crumpled into a ball?

Q 44.

The volume of a 500 g sealed packet is 350 cm³. Will the packet float or sink in water if the density of water is 1 g cm^-3? What will be the mass of the water displaced by this packet?

Q 45.

Why is it difficult to hold a school bag having a strap made of a thin and strong string?

Q 46.

As you climb up a mountain, your ears “pop” because of the changes in atmospheric pressure. In which direction, outward or inward, does your eardrum move when you climb up?

Q 47.

A stone drops from the edge of the roof.It passes a window 2 m high in 0.1 s.How far is the roof above the top of the window

Q 48.

A force of 20 N acts upon a body whose weight is 9.8 N.What is the mass of the body and how much is its acceleration ?

Q 49.

What are the differences between the mass of an object and its weight ?

Q 50.

What is the magnitude of the gravitational force between the Earth and a 1 kg on its surface ? (Mass of the Earth Is $6x1024$ kg and radius of the Earth is $6.4x106$m.)