Gravitation

Q 1.

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

Q 2.

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

Q 3.

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 4.

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 5.

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 6.

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 7.

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

Q 8.

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 9.

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

Q 10.

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

Q 11.

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 12.

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

Q 13.

What do you mean by acceleration due to gravity ?

Q 14.

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

Q 15.

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

Q 16.

State and explain universal law of gravitation given by Newton.What is the importance of this law

Q 17.

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 18.

The mass of Sun is $2x1030$ kg and mass of Earth is $6x1024$ kg. If the distance between the centres of Sun and Earth is $1.5x1080$ km,calculate the force of gravitation between them.

Q 19.

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.)

Q 20.

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 21.

Write the standard equations of motion when an object is thrown upwards with some initial velocity?

Q 22.

A ball is thrown with some velocity 'u' m/s. Show that under free fall, it will fall the ground with same velocity.

Q 23.

Why does a block of plastic released under water come up to 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 importance of universal law of gravitation ?

Q 26.

A body is projected upwards. What is its velocity at maximum height

Q 27.

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

Q 28.

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

Q 29.

The earth and the moon are attracted to each other by gravitational force. Does the earth attract the moon with a force that is greater or smaller or the same as the force with whichthe moon attracts the earth? Why?

Q 30.

Define 'g' or acceleration due to gravity? Does it depend on the mass of the body (near the surface of the earth)experiencing 'g'?

Q 31.

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

Q 32.

Gravitational force on the surface of the moon is only 1/6th as strong as gravitational force on the Earth. What is the weight in newtons of a 10 kg object on the moon and on the Earth? What is the value of 'g' at the surface of the moon?

Q 33.

The tangential velocity of a planet or moon moving in a circle is at a right angle to ____________. (fill in the blank)

Q 34.

Fill in the blanks :
Universal gravitational constant G = _____________.

Q 35.

The weight of a man is 690N which contains 5.3 x 10^-3 m³ of blood. Find (a) blood's weight. Take density of blood is 1060 kg/m³ (b) express it as a percentage of body weight.

Q 36.

You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?

Q 37.

Calculate the force of gravitation between two objects of masses 80 kg and 1200 kg kept at a distance of 10 m from eachother.Given, G =$6.67x10-11$ $Nm2$/$kg2$.

Q 38.

State the universal law of gravitation.

Q 39.

Does Newton’s third law of motion apply to gravitational force ?

Q 40.

Fill in the blanks :
The force which keeps the object moving in a circular path is called _____ force. It always acts towards the _____.

Q 41.

Write the standard equations in the form when an object is dropped from a height?

Q 42.

Fill in the blanks :
The force of gravity _________ with altitude. It also varies on the surface of the earth, _________ from poles to the equator.

Q 43.

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 44.

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 45.

A cuboid room has dimensions 50m x 15m x 3.5m. What is the mass of the air enclosed in the room if the density of air = 1.30 kg/m³.

Q 46.

The distance of planet Jupiter from the sun is 5-2 times that of Earth.Find the period of revolution of Jupiter around sun.

Q 47.

A force of 2 kg wt. acts on a body of mass 4.9 kg.Calculate its acceleration

Q 48.

Two objects of masses $m$₁ and m₂ having the same size are dropped simultaneously from heights $h$₁ and h₂ respectively.Find out the ratio of time they would take in reaching the ground.Will this ratio remain the same if (1) one of the objects is hollow and the other one is solid and (ii) both of them are hollow,size remaining the same in each case.Give reason.

Q 49.

Can a body have mass but no weight ?

Q 50.

Can a body have weight but no mass ?