Lakhmir Singh Solutions - Physics- Class 9 solutions for Chapter 3 Gravitation

What is the value of gravitational constant G

a) on the earth

b) on the moon

When an object is dropped from a height, it accelerates and falls down. Name the force which accelerates the object.

Give the formula for the gravitational force F between two bodies of masses M and m kept at a distance d from each other.

What force is responsible for the earth revolving round the sun?

What name has been given to the force with which two objects lying apart attract each other?

What type of force is involved in the formation of tides in the sea?

Which force is responsible for holding the solar system together?

What is the weight of a 1kg mass of the earth? When g = 9.8 $\mathrm{m/ s^2}$ .

On what factor/factors does the weight of a body depend?

As the altitude of a body increases, do the weight and mass both vary?

If the same body is taken to places having different gravitational field strength, then what will vary: its weight or mass?

Which force is responsible for the moon revolving around the earth?

If the mass of an object be 10kg what is its weight?

The weight of a body is 50N. What is its mass?

A body has a weight of 10kg on the surface of the earth. What will be its weight when taken to the centre of the earth?

Write down the weight of a 50kg mass on the earth.

If the weight of a body on the earth is 6N, what will be on the moon?

State whether the following statements are true or false.

a) A falling stone also attracts the earth.

b) The force of gravitation between two objects depends on the nature of the medium between them.

c) The value of G on the moon is about one-sixth of the value of G on the earth.

d) The acceleration due to gravity acting on a freely falling body is directly proportional to the mass of the body.

e) The weight of an object on the earth is about one-sixth of the weight on the moon.

Does the acceleration produced in a freely falling body depend on the mass of the body?

Name the scientist who gave the three laws of planetary motion.

Name the scientist who explained the motion of planets on the basis of the gravitational force between the sun and the planets.

State the Kepler’s law which is represented by the relation $\mathrm {r^3 \propto T^3}$ .

Which of the Kepler’s laws of planetary motion led Newton to establish the inverse-square rule for gravitational force between two bodies?

Name the property of earth which is responsible for extremely small acceleration being produced in it as a result of attraction by other small objects.

What is the acceleration produced in a freely falling body of mass 10kg?

Fill in the blanks with suitable words:

a) The acceleration due to gravity on the moon is about ________ of that on the earth.

b) In order that the force of gravitation between two bodies may become noticeable and cause motion, one of the bodies must have an extremely large _______

c) The weight of an object on the earth is about ________ of its weight on the moon.

d) The weight of an object on the moon is about _________ of its weight on the earth.

e) The value of g on the earth is about ________ of that on the moon.

f) If the weight of a body is 6N on the moon, it will be about ________ on the earth.

Explain what is meant by $\mathrm{g=G(M/R^2)}$ where the symbols have their usual meanings

a) What do you mean by the term free fall?

b) During a free fall, will heavier objects accelerate more than the lighter ones?

Can we apply Newton’s third law to the gravitational force? Explain your answer.

Give a reason for the following:

The force of gravitation between two cricket balls is extremely small but that between a cricket ball and the earth is extremely large.

Describe how the gravitational force between two objects depends on the distance between them.

What happens to the gravitational force between two objects when the distance between them is:

a) Doubled?

b) Halved?

State two applications of the universal law of gravitation.

Explain why if a stone held in our hand is released, it falls towards the earth.

Calculate the force of gravitation between two objects of masses 50kg and 120kg respectively kept at a distance of 10m from one another.

What is the force of gravity on a body of mass 150 kg lying on the surface of the earth? Assume mass of the earth = 6 × $10^{24}$ kg, radius of the earth = 6.4 × $10^6$ m, and G = $6.7 \times 10^{-11} \mathrm{Nm}^{2} / \mathrm{kg}^{2}$ .

The mass of the sun is 2 × $10^{30}$ kg and the mass of the earth is 6 × $10^{24}$ kg. If the average distance between the sun and the earth be 1.5 × $10^8$ km, calculate the force of gravitation between them.

A piece of stone is thrown vertically upwards. It reaches the maximum height in 3 seconds. If the acceleration of the stone be 9.8 $m/s^2$ directed towards the ground, calculate the initial velocity of the same with which it is thrown upwards.

A stone falls from a building and reaches the ground in 2.5 seconds later. How high is the building?

When is the work done by a force on a body:

a) positive

b) negative

c) zero

A stone is dropped from a height of 20m.

a) How long will it take to reach the ground?

b) What will be its speed when it hits the ground?

A stone is thrown vertically upwards with a speed of 20m/s. How high will it go before it beings to fall?

When a cricket ball is thrown vertically upwards, it reaches a maximum height of 5 meters.

a) What was the initial speed of the ball?

b) How much time is taken by the ball to reach the highest point?

Write the difference between mass and weight of an object.

Can a body have mass but no weight? Give reasons for your answer.

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

A stone resting on the ground has a gravitational force of 20N acting on it. What is the weight of the stone? What is its mass?

An object has a mass of 20 kg on the earth. What will be its

a) mass

b) weight on the moon.

Which is more fundamental, the mass of a body or its weight? Why?

How much is the weight of an object on the moon as compared to its weight on the earth? Give a reason for your answer.

a) Define the mass of a body. What is the SI unit of mass?

b) Define the weight of a body. What is the SI unit of weight?

c) What is the relation between the mass and weight of a body?

a) State the universal law of gravitation. Name the scientist who gave this law.

b) Define gravitational constant. What are the units of gravitational constant?

a) What do you understand by the term ‘acceleration due to gravity of earth’?

b) What is the usual value of acceleration due to gravity of earth?

c) State the SI unit of acceleration due to gravity.

a) Is the acceleration due to the gravity of earth ‘g’ a constant? Discuss.

b) Calculate the acceleration due to gravity on the surface of a satellite having a mass of $7.4\ \times10^{22\ }$ kg and a radius of $1.74\times10^6$ m. Which satellite do you think it could be?

State and explain Kepler’s laws of planetary motion. Draw diagrams to illustrate these laws.

The mass of a planet is $6\times10^{24}$ kg and its diameter is $12.8\times10^3$ km. If the value of a gravitational constant is $6.7\times10^{-11}Nm^2/kg^2$ , Calculate the value of acceleration due to gravity on the surface of the planet. What planet could this be?

An object is thrown vertically upwards with a velocity u, the greatest height h to which it will rise before falling back is given by:

a) u/g

b) $u^2/2g$

c) $u^2/g$

d) u/2g

The mass of the moon is about 0.012 times that of the earth and its diameter is about 0.25 times that of earth. The value of G on the moon will be:

a) less than that on the earth

b) more than that on the earth

c) same as that on the earth

d) about one-sixth of that on the earth

The atmosphere consisting of a large number of gases is held to the earth by:

a) Winds

b) Clouds

c) Earth’s magnetic field

d) Gravity

The force of attraction between two unit point masses separated by a unit distance is called:

a) Gravitational potential

b) Acceleration due to gravity

c) Gravitational field strength

d) Universal gravitational constant

The weight of an object at the centre of the earth of radius R is:

a) Zero

b) R times the weight at the surface of the earth

c) Infinite

d) $1/R^2$ times the weight at the surface of the earth

Two objects of different masses falling freely near the surface of the moon would:

a) Have the same velocities at any instant

b) Have different accelerations

c) Experience forces of the same magnitude

d) Undergo a change in their inertia

The value of acceleration due to gravity of earth:

a) Is the same on equator and poles

b) Is the least on poles

c) is the least on the equator

d) Increases from pole to equator

The law of gravitation gives the gravitational force between:

a) The earth and a point mass only

b) The earth and the sun only

c) Any two bodies having some mass

d) Any two charged bodies only

The value of quantity G in the formula for gravitational force:

a) depends on the mass of the earth only

b) depends on the radius of the earth only

c) depends on both mass and radius of the earth

d) depends neither on mass nor on the radius of the earth

Two particles are placed at some distance from each other. If keeping the distance between them unchanged the mass of each of the two particles is doubled, the value of gravitational force between them will become:

a) ¼ times

b) ½ times

c) 4 times

d) 2 times

In the relation F = (G)(M)(m/d2) the quantity G:

a) Depends on the value of g at the place of observation

b) Is used only when the earth is one of the two masses

c) Is the greatest on the surface of the earth

d) Is of the same value irrespective of the place of observation

The gravitational force of attraction between two objects is x. Keeping the masses of the objects unchanged, if the distance between the objects are halved, then the magnitude of the gravitational force between them will become:

a) x/4

b) x/2

c) 2x

d) 4x

An apple of mass 100g falls from a tress because of gravitational attraction between the earth and the apple. If the magnitude of the force exerted by the earth on the apple be F1 and the magnitude of the force exerted by the apple on the earth be F2, then:

a) F1 is very much greater than F2

b) F2 is very much greater than F1

c) F1 is only a little greater than F2

d) F1 and F2 are exactly equal

According to one of the Kepler’s laws of planetary motion:

a) $r^2\proptoT^3$

b) $r\proptoT^2$

c) $r^3\proptoT^2$

d) $r^3\propto1/T^2$

Lakhmir singh solutions physics class 9 Solutions for Chapter 3 gravitation