Gravitation (Test -1) - Class 9 Science, 21-02-2018 - Class 9 MCQ

Universal gravitational constant is represented by ‘G’. S.I. unit of universal gravitational constant is Nm²/kg² 

As G=Fxr²/Mm.

Gravitational force acts between two bodies to attract the bodies towards each other. Tides in ocean, movement of satellite and rain fall is not due to gravitational force.

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.

The force acting on two bodies is inversely proportional to square of the distance between them. Therefore, Fα 1/r².

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.

Initial velocity ,u= 20 m/s. final velocity= o , g =10ms−210ms⁻² . V = u + gt, 0=20+(−10)×t, t= 20/10 = 2s. time taken to fall in downward direction = 2s. hence total time taken = 2s +2s = 4s.

Force of gravitation is equal to product of masses divided by square of the distance between them. So, force of gravitation between two bodies will be same irrespective of their place. Ratio will be 1:1.

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.

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.

Pressure = force/ area. Here, Force = 200N. Area=5m². So, pressure = 200N/5m² = 40 Pa.

The value of universal gravitational constant (G) is6.67×10⁻¹¹Nm²/Kg². Which is constant and independent of mass, distance between the bodies and other factors.

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

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

Gravitational force between two bodies F =G 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.

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.

The force of attraction is always attractive. Law of inverse square means that the force by which two objects attracts each other is inversely proportional to square of the distance between them.

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.

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.

According to universal law of gravitation the force is directly proportional to product of their masses and inversely proportional to square of the distance between them.

Value of acceleration due to gravity (g) =GM/r². Suppose a planet starts shrinking the value of ‘g’ will increase accordingly. As the radius is decreasing the g will increase proportionally.

Weight of the body is equal to product of mass and acceleration due to gravity.=Kg×m/s²= N (Newton).

The value of G, universal gravitational constant remain same everywhere. So, value of G is equal at both earth and moon. Hence, above statement is false.

Acceleration due to gravity is independent of mass of the object. Two bodies having different mass kept on earth will have equal acceleration due to gravity as g =GM/r².