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NCERT Solutions for Class 9 Science Chapter 10 Gravitation

NCERT Solutions for Class 9 Science Chapter 10 Gravitation

NCERT Solutions for Class 9 Science Chapter 10 Gravitation

 

Class 9 Science NCERT Textbook Page 134

 

Question:- 1. State the universal law of gravitation.

Answer:-  According to the universal law of gravity, every object in the universe attracts every other object through a force known as gravitational attraction. The force acting between two objects is proportional to the product of their masses and inversely proportional to the square of their distance.

 

Question:- 2. Write the formula to find the magnitude of the gravitational force between the earth and an object on the surface of the earth.

Answer:- F = G Mm/R2

Where, F=  force of attraction between the earth and an object on the surface of the earth

m = Mass of the object on the surface of the earth.

M = Mass of the earth.

R = Distance between the earth’s centre and object.

 

Class 9 Science NCERT Textbook Page 136

Question:- 1. What do you mean by free fall?

Answer:- Every thing is attracted to the earth’s centre by gravity. When an object is dropped from a specific height, gravitational force causes it to fall towards the Earth’s surface. The motion of an object in this manner is known as free fall.

 

Question:- 2. What do you mean by acceleration due to gravity?

Answer:- The velocity of an object changes when it falls freely towards the earth’s surface from a specific height. This change in velocity causes the item to accelerate, which is known as acceleration due to gravity, and is symbolised by the letter ‘g’.

g=9.8 m/s2 is the value of gravity acceleration.

 

Class 9 Science NCERT Textbook Page 138

 

 

Question:- 1. What are the differences between the mass of an object and its weight?

Answer:-

Mass

Weight

Mass is the quantity of matter contained in the body.

Weight is the force of gravity acting on the body.

It is the measure of inertia of the body.

It is the measure of gravity.

It only has magnitude.

It has magnitude as well as direction.

Mass is a constant quantity.

Weight is not a constant quantity. It is different at different places.

Its SI unit is kilogram (kg).

Its SI unit is the same as the SI unit of force, i.e., Newton (N).

 

Question:- 2. Why is the weight of an object on the moon 1/6th its weight on the earth?

Answer:- The moon’s mass is 1/100 that of the earth, while its radius is 1/4 that of the earth. As a result, the moon’s gravitational attraction is about one-sixth that of the Earth. As a result, the weight of an object on the moon is 1/6 that of an object on Earth.

 

Class 9 Science NCERT Textbook Page 141

 

Question:- 1. Why is it difficult to hold a school bag having a strap made of a thin and strong string?

Answer:-  Because the force exerted by a thin and strong string is distributed over a smaller area, the force applied by the bag is more, the pressure imposed on the body by thin straps is greater, and thus the pain is greater.

As pressure is inversely related to area, pressure rises when the area is reduced.

 

Question:- 2. What do you mean by buoyancy?

Answer:-   Upthrust or buoyancy refers to the upward force exerted by any fluid (liquid, gas) on an object.

 

Question:- 3. Why does an object float or sink when placed on the surface of water?

Answer:-  When an object is placed on the surface of water, its density determines whether it will float or sink. When the density of an object is less than that of water, the object will floats and if its density is greater than the density of water then it will sink.

 

Class 9 Science NCERT Textbook Page 142

 

Question:- 1. You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?

Answer:-  The weighing machine actually measures the body’s weight as the acceleration due to gravity, or ‘g,’ acts on it. As a result, a weighing machine’s mass reading of 42 kg corresponds to the body’s real mass. It remains the same since mass is the quantity of inertia.

 

Question:- 2. You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why?

Answer:- The heaviness of the bag can be given by density

Density= mass/volume

Cotton and iron bags have the same mass. However, the cotton bag has a larger volume than the iron bag. As a result, density and volume are inversely proportionate. The iron bag will be larger.

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