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QUESTION: 1

The S. I unit of G is

Solution:

Universal gravitational constant is represented by ‘G’. S.I. unit of universal gravitational constant is Nm^{2}/Kg^{2}. As G = Fxr^{2}/Mm.

QUESTION: 2

The mass of the body on the moon is 40kg, what is the weight on the earth.

Solution:

Given The mass of the body on moon is 40 kg , what is the weight on the earth ?

Now we have mass of body on moon m = 40 kg.

We know that weight on earth is given by mass x gravitational force

So w = m x g

w = 40 x 9.8 m/s^{2}

w = 392 N

So weight on the earth is 392 N

QUESTION: 3

A body is thrown upwards. What is the direction of ‘g’ when the body is falling down

Solution:

When a body is thrown upwards, the direction of ‘g ‘ is negative that slows down the speed of body. When the body is falling downward, the direction of ‘g’ is downward direction.

QUESTION: 4

Two objects of different masses are dropped freely from a height near the surface of earth they have

A. Different velocities at any instant

B. Same velocities at any instant

C. Different accelerations

D. Same acceleration

Solution:

The correct option is B.

Objects of different masses falling freely near the surface of the earth would have the same velocities at any instant because they will have the same acceleration due to gravity.

QUESTION: 5

Inverse square law means F α?

Solution:

The force acting on two bodies is inversely proportional to square of the distance between them. Therefore,Fα 1/r^{2}.

QUESTION: 6

Statement A: Polar radius is 6357km and equatorial radius is 6378km,

Statement B: At a given place the weight of an object is equal to mass of the objectWhich of the two statement is true?

Solution:

Polar radius is 6357 km and equatorial radius is 6378 km. The shape of earth is not perfectly spherical. Poles are slightly closer to centre of earth. Weight of body at particular place is product of mass and acceleration due to gravity. So, weight and mass of body at particular position never be equal.

QUESTION: 7

A man throws a ball with a velocity of 20m/s. After what time will the ball come back to his hands? (Take g = 10m/s^{2})

Solution:

Initial velocity ,u= 20 m/s. final velocity = o , g = 10ms^{−2} . V = u + gt, 0 = 20+(−10)×t20+(−10)×t, t = 20/10 = 2s. time taken to fall in downward direction = 2s. hence total time taken = 2s +2s = 4s.

QUESTION: 8

A stone falling towards earth

A. Is attracted by earth

B. Attracts the earth

C. Both stone and earth attract each other

D. No one attract each other

Solution:

QUESTION: 9

What is ratio of the force of gravitation between two mases m^{1 }and m^{2} Kept at a distance R on the Earth and on the moon?

Solution:

**Correct Answer :- b**

**Explanation:- Force of gravitation is equal to product of masses divided by square of the distance between them. So, the force of gravitation between two bodies will be the same irrespective of their place. **

**So, the ratio will be 1:1.**

QUESTION: 10

Gravitation force is a

Solution:

Gravitational force is a weak force. This force exists between each and every object but cannot be felt until the mass of the bodies are not extremely high like planets.

QUESTION: 11

“The equation of motion for free fall can be used in case of any free fall” is

Solution:

The equation of motion for free fall can be used in case of falling of body only due to gravitation of earth without any other force. So, this statement is not true.

QUESTION: 12

What will be the pressure when a force of 200N it’s exerted on area of 5m^{2}

Solution:

Pressure = force/ area. Here, Force = 200N. Area=5m^{2}. So, pressure = 200N/5m 25m^{2} = 40 Pa.

QUESTION: 13

The value of G depends on

Solution:

The value of universal gravitational constant (G) is6.67×10^{−11}Nm^{2}/Kg^{2 } Which is constant and independent of mass, distance between the bodies and other factors.

QUESTION: 14

Statement A: The Earth attract the moon with a force greater than the force with which the moon attracts the Earth.

Statement B: The mass and weight of a body becomes O at the centre of the Earth.

Which of the two statement is true?

Solution:

Earth and moon attracts each other with equal gravitational force. The mass of a body never becomes 0. Hence both statements are incorrect.

QUESTION: 15

What is the weight of body whose mass is 100 kg. on the surface of the earth

Solution:

Mass of the body (m) = 100 kg, acceleration due to gravity (g) =9.8 m/s29.8 m/s2. Weight (w) = m×gm×g=100×9.8100×9.8= 980N.

QUESTION: 16

In which of the following pressure is increased

A. Strap of bag is made wider

B. Knife with sharp edge

C. Shoes with flat sole

D. Nail with finely pointed tip

Solution:

QUESTION: 17

Two masses m and M are kept at a distance r. The ratio of the force exerted on m due to M and that of M due to m is equal to

Solution:

Gravitational force between two bodies F = G Mm/r2G Mm/r2. The value of force exerted on m due to M will be equal to that of M due to m. so, the ratio will be 1;1.

QUESTION: 18

Force of gravitation

A. Directly proportional to the product of masses of two objects

B. Inversely proportional to the product of masses of two objects

C. Directly proportional to the square of distance between two objects

D. Inversely proportional to the square of distance between two objects

Solution:

QUESTION: 19

The weight of an object is least at some region of the earth. What will be the colour of bears found in that region.

Solution:

The weight of the body is the measure of force by which earth attracts the body. Acceleration due to gravity is less in case of poles and colour of bears found in these regions are white, called as polar bear.

QUESTION: 20

What is buoyant force-

Solution:

The upward force experienced by the body when partially or completely submersed in fluid.

QUESTION: 21

Which of the two statements is true?

Statement A: The force of gravitation may be attractive or repulsive.

Statement B: Inverse square law means

Solution:

Gravitational force is always attractive in nature irrespective of the distance and mass of bodies. this decreases with distance but cannot be repulsive.

In science, an inverse-square law is any scientific law stating that a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity.Since the gravitational field lines go radially inward towards the mass, the density of the field lines would be inversely proportional to the surface over which they are spread over and therefore inversely proportional to r^2. Since force is proportional to the density of field lines, the force is inversely proportional to distance squared.

QUESTION: 22

Which of the following is an application of Earth’s gravitation

A. It holds atmosphere around our globe

B. It holds us firmly on the surface of the Earth

C. It is responsible for motion of moon

D. It is responsible for sea tides due to the moon

Solution:

QUESTION: 23

An object weighs 10N when measured on the surface of the Earth. What would be its weight when measured on the surface of the moon?

Solution:

Acceleration due to gravity (g) on moon is 1/6^{th} of the acceleration of gravity (g) on earth. So, weight of body of 10N on the surface of moon will be 1/6×10N = 1.67N.

QUESTION: 24

Find the incorrect statement.

Solution:

Value of g depends upon mass of the planet and radius, acceleration due to gravity does not change due to air friction. Body moving in upward direction will have gravitational force in downward direction.

Mass is a scalar quantity. It is a measure of the inertia of an object. Mass can be represented by a number only. The SI unit of mass is kg.

QUESTION: 25

According universal law of Gravitation

(i) Force is directly proportional to product of masses of two bodies

(ii) Force is inversely proportional to square of distance between two bodies

(iii) Force is directly proportional to square of distance between two bodies

(iv) Force is inversely proportional to product of masses of two bodies

Solution:

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