The document Solution of Gravitation (Page No - 100) - Physics by Lakhmir Singh, Class 9 Class 9 Notes | EduRev is a part of the Class 9 Course Class 9 Physics Solutions By Lakhmir Singh & Manjit Kaur.

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__Page No - 100__

**Question 1:**

Value of gravitational constant G on the earth and the moon is = 6.67 x 10

Note that the value of G always remains constant irrespective of the location.

**Question 2:****Which force is responsible for the moon revolving round the earth ?****Solution :**

Gravitational force is responsible for the moon revolving round the earth.

**Question 3:****Does the acceleration produced in a freely falling body depend on the mass of the body ?****Solution :**

No, the acceleration produced in a freely falling body is independent of the mass of the body.

**Question 4:****Name the scientist who gave the three laws of planetary motion.****Solution :**

Johannes Kepler gave the three laws of planetary motion.

**Question 5:****Name the scientist who explained the motion of planets on the basis of gravitational force between the sun and planets.**

Newton explained the motion of planets on the basis of gravitational force between the sun and planets.

**Question 6:****State the Kepler’s law which is represented by the relation r ^{3} ∝ T^{2}.**

Kepler’s law of periods states that: The cube of the mean distance of a planet from the sun is directly proportional to the square of time it takes to move around the sun.

**Question 7:****Which of the Kepler’s laws of planetary motion led Newton to establish the inverse-square rule for gravitational force between two bodies ?****Solution :**

Kepler’s third law of planetary motion led Newton to establish the inverse-square rule for gravitational force between two bodies.

**Question 8:****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.****Solution :**

Extremely large mass of the earth.

**Question 9:****What is the acceleration produced in a freely falling body of mass 10 kg ? (Neglect air resistance)**

Acceleration produced in a freely falling body, irrespective of its mass, is 9.8m/s

**Question 10:****When an object is dropped from a height, it accelerates and falls down. Name the force which accelerates the object.****Solution :**

Gravitational force of the earth.

**Question 11:****Give the formula for the gravitational force F between two bodies of masses M and m kept at a distance d from each other.****Solution :**

The gravitational force F between two bodies of masses M and m kept at a distance d from each other is :

Here, Gravitational Constant, G= 6.7x 10^{-11}Nm^{2}kg^{-}^{2}

**Question 12:**

What force is responsible for the earth revolving round the sun ?**Solution :**

Gravitational force is responsible for the earth revolving round the sun.

**Question 13:**

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

Gravitational force causes two objects lying apart attract each other.

**Question 14:**

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

Gravitational force (exerted mainly by the moon and to some extent by the sun) is involved in the formation of tides in the sea.

**Question 15:**

Which force is responsible for holding the solar system together ?**Solution :**

Gravitational force of the sun holds the solar system together.

**Question 16:**

What is the weight of a 1 kilogram mass on the earth ? (g = 9.8 m/s^{2}).**Solution :**

Weight, W = m x g

= 1 kg x 9.8m/s^{2}=9.8 N

**Question 17:**

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

The weight of a body is directly proportional to its mass. It also depends on the acceleration due to gravity which varies from place to place.

**Question 18:**

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

Weight of the body varies with altitude; mass of an object is constant.

**Question 19:**

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

Its weight varies; mass of an object is constant.

**Question 20:**

If the mass of an object be 10 kg, what is its weight ? (g = 9.8 m/s^{2}).**Solution :**

Weight, W = m x g = 10 x 9.8 =98 N

**Question 21:**

The weight of a body is 50 N. What is its mass ? (g = 9.8 m/s^{2}).**Solution :**

Weight, W = m x g

**Question 22:**

A body has a weight of 10 kg on the surface of earth. What will be its weight when taken to the centre of the earth ?**Solution :**Its weight will be zero as value of g is zero at the centre of the earth.

**Question 23:**

Write down the weight of a 50 kg mass on the earth, (g = 9.8 m/s^{2}).**Solution :**

Weight, W= m x g =50 x 9.8=490N

**Question 24:**

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

Weight of the body on the surface of moon will be 1N approx. as the value of g on the surface of moon is one-sixth that of the earth

**Question 25:**

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 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) Tire weight of an object on the earth is about one-sixth of its weight on the moon.

**Solution :**

(a)True

(b)False

(c)False

(d)False

(e) False

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