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ScienceClass 9CBSE

The weight of any person on the moon is about 1/6 times that on the earth. He can lift a mass of 15 kg on the earth. What will be the maximum mass, which can be lifted by the same force applied by the person on the moon?

Soln: Weight of person is = 1/6th of weight on earth This proves acceleration due to gravity on moon is 1/6th of acceleration due to gravity on earth. Hence the person can lift a mass 6 times heavier on moon than on earth.

ScienceClass 9CBSE

Identical packets are dropped from two aeroplanes, one above the equator and the other above the north pole, both at height h. Assuming all conditions are identical, will those packets take same time to reach the surface of earth. Justify your answer.

Soln: Value of g is greater than value of g in poles . Since packets are thrown from same height packet thrown froom poles reaches the earth first.

ScienceClass 9CBSE

Suppose gravity of earth suddenly becomes zero, then in which direction will the moon begin to move if no other celestial body affects it?

Soln: If there is no gravitational pull from the earth moon start to move in a straight line tangent to its circular path.

ScienceClass 9CBSE

On the earth, a stone is thrown from a height in a direction parallel to the earth’s surface while another stone is simultaneously dropped from the same height. Which stone would reach the ground first and why?

Soln: Both the stones reach the ground simultaneously as they are dropped from same height and their intial velocity will be same .

ScienceClass 9CBSE

What is the source of centripetal force that a planet requires to revolve around the Sun? On what factors does that force depend?

Soln: Gravitational force is the source of centripetal force required to revolve around the sun. This force depends on distance between the planet and sun along with their masses.

ScienceClass 9CBSE

An apple falls from a tree because of gravitational attraction between the earth and apple. If F1 is the magnitude of force exerted by the earth on the apple and F2 is the magnitude of force exerted by apple on earth, 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 F1 and F2 are equal

Soln: Answer is (d) F1 and F2 are equal Explanation: Netwon’s third law of motion states that for every action there is equal and opposite reaction. Hence F1 and F2 are equal.

ScienceClass 9CBSE

A girl stands on a box having 60 cm length, 40 cm breadth and 20 cm width in three ways. In which of the following cases, pressure exerted by the brick will be (a) maximum when length and breadth form the base (b) maximum when breadth and width form the base (c) maximum when width and length form the base the same in all the above three cases

Soln: Answer is (b) maximum when breadth and width form the base Explanation: Surface area and pressure are inversely proportional. Pressure will be maximum when surface area is minimum hence the answer is maximum when breadth and width form the base

ScienceClass 9CBSE

An object weighs 10 N in air. When immersed fully in water, it weighs only 8 N. The weight of the liquid displaced by the object will be (a) 2 N (b) 8 N (c) 10 N (d) 12 N

Soln: Answer is (a) 2 N Explanation: Object of weight displace d by liquid = weight in air- weight in liquid =10N-8N = 2N

ScienceClass 9CBSE

The weight of an object at the centre of the earth of radius R is (a) zero (b) infinite (c) R times the weight at the surface of the earth 1/R2 times the weight at surface of the earth

Soln: Answer is (a) zero Explanation: At the centre of the earth acceleration due to gravity is zero . Since weight is the product of mass and gravity. Weight of object at the centre of the earth will be zero.

ScienceClass 9CBSE

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 universal gravitational constant

Soln: Answer is (d) universal gravitational constant Explanation: F= Gx𝑚1𝑥𝑚2 𝑟2 Here point masses are separated by unit distance Hence m1, m2 and r = 1 Hence F=G which is a universal constant hence answer is universal gravitational constant

ScienceClass 9CBSE

The atmosphere is held to the earth by (a) gravity (b) wind (c) clouds earth’s magnetic field

Soln: Answer is (a) gravity

ScienceClass 9CBSE

1. Two particles are placed at some distance. If the mass of each of the two particles is doubled, keeping the distance between them unchanged, the value of gravitational force between them will be (a) 1 4 times (b) 4 times (c) 1 2 times unchanged

<ul><li>Soln:</li></ul>Answer is (b) 4 timesExplanation:F= Gx𝑚1𝑥𝑚2𝑟2F=Gx2𝑚1𝑥2𝑚2𝑟2F= 4xGx𝑚1𝑥𝑚2𝑟2

ScienceClass 9CBSE

The value of quantity G in the law of gravitation (a) depends on mass of earth only (b) depends on radius of earth only (c) depends on both mass and radius of earth is independent of mass and radius of the earth

Soln: Answer is (d) is independent of mass and radius of the earth Explanation: G is an universal constant hence it is independent of mass and radius of the earth.

ScienceClass 9CBSE

Law of gravitation gives the gravitational force between (a) the earth and a point mass only (b) the earth and Sun only (c) any two bodies having some mass two charged bodies only

Soln: Answer is (c) any two bodies having some mass

ScienceClass 9CBSE

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 greatest at the surface of the earth is universal constant of nature

Soln: Answer is (d) is universal constant of nature Explanation: G is called as Newton’s constant. It is the force of gravity on a body. Value of G is 6.66x 10-11 Nm2kg-2

ScienceClass 9CBSE

An object is put one by one in three liquids having different densities. The object floats with 12 3 , and 9 11 7 parts of their volumes outside the liquid surface in liquids of densities d1, d2 and d3 respectively. Which of the following statement is correct? (a) d1> d2> d3 (b) d1> d2 d3 d1< d2< d3

Soln: Answer is (d) d1< d2< d3

ScienceClass 9CBSE

A boy is whirling a stone tied with a string in an horizontal circular path. If the string breaks, the stone (a) will continue to move in the circular path (b) will move along a straight line towards the centre of the circular path (c) will move along a straight line tangential to the circular path will move along a straight line perpendicular to the circular path away from the boy

Soln: Answer is (c) will move along a straight line tangential to the circular path Explanation: At any instance of time object in circular motion tend to be in rectilinear motion. Object keeps on moving due to centripetal force and it moves along a straight line tangential to the circular path when strings breaks.

ScienceClass 9CBSE

The gravitational force between two objects is F. If masses of both objects are halved without changing distance between them, then the gravitational force would become (a) F/4 (b) F/2 (c) F (d) 2 F

Soln: Answer is (a) F/4

ScienceClass 9CBSE

The value of acceleration due to gravity (a) is same on equator and poles (b) is least on poles (c) is least on equator increases from pole to equator

Soln: Answer is (c) is least on equator Explanation: The value of acceleration due to gravity is least on equator because distance between surface of the earth and its centre is more on equator than in poles.

ScienceClass 9CBSE

Two objects of different masses falling freely near the surface of moon would (a) have same velocities at any instant (b) have different accelerations (c) experience forces of same magnitude undergo a change in their inertia

Soln: Answer is (a) have same velocities at any instant Explanation: Acceleration of an object depends on acceleration due to gravity irrespective of its mass. Hence object under free fall have the same velocities.

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Filtered results

The weight of any person on the moon is about 1/6 times that on the earth. He can lift a mass of 15 kg on the earth. What will be the maximum mass, which can be lifted by the same force applied by the person on the moon?

Identical packets are dropped from two aeroplanes, one above the equator and the other above the north pole, both at height h. Assuming all conditions are identical, will those packets take same time to reach the surface of earth. Justify your answer.

Suppose gravity of earth suddenly becomes zero, then in which direction will the moon begin to move if no other celestial body affects it?

On the earth, a stone is thrown from a height in a direction parallel to the earth’s surface while another stone is simultaneously dropped from the same height. Which stone would reach the ground first and why?

What is the source of centripetal force that a planet requires to revolve around the Sun? On what factors does that force depend?

An object weighs 10 N in air. When immersed fully in water, it weighs only 8 N. The weight of the liquid displaced by the object will be (a) 2 N (b) 8 N (c) 10 N (d) 12 N

The weight of an object at the centre of the earth of radius R is (a) zero (b) infinite (c) R times the weight at the surface of the earth 1/R2 times the weight at surface of the earth

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 universal gravitational constant

The atmosphere is held to the earth by (a) gravity (b) wind (c) clouds earth’s magnetic field

1. Two particles are placed at some distance. If the mass of each of the two particles is doubled, keeping the distance between them unchanged, the value of gravitational force between them will be (a) 1 4 times (b) 4 times (c) 1 2 times unchanged

The value of quantity G in the law of gravitation (a) depends on mass of earth only (b) depends on radius of earth only (c) depends on both mass and radius of earth is independent of mass and radius of the earth

Law of gravitation gives the gravitational force between (a) the earth and a point mass only (b) the earth and Sun only (c) any two bodies having some mass two charged bodies only

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 greatest at the surface of the earth is universal constant of nature

The gravitational force between two objects is F. If masses of both objects are halved without changing distance between them, then the gravitational force would become (a) F/4 (b) F/2 (c) F (d) 2 F

The value of acceleration due to gravity (a) is same on equator and poles (b) is least on poles (c) is least on equator increases from pole to equator

Two objects of different masses falling freely near the surface of moon would (a) have same velocities at any instant (b) have different accelerations (c) experience forces of same magnitude undergo a change in their inertia

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