Motion Under Gravity

Total Questions: 41

21. If the radius of the earth were to shrink by one percent its mass remaining the same the value of g on the earths surface would : [I.A.S. (PRE) 2003]

(a) increase by 0.5%
(b) increase by 2%
(c) decrease by 0.5%
(d) decrease by 2%

Correct Answer: (b) increase by 2%

Solution:we know that g=GM/R² ..........(1)
After shrinking by 1% new radius will be 0.99 R
Then g'=GM/(0.99R)² ...........(2)

g'/g=R²/(0.99R)² =1/0.99)² =1.02

From the equation (1) and (2) we get

g'=1.02g
thus the value of g is increased by 2%

22. The acceleration due to gravity of a destructive earthquake will be - [I.A.S. (PRE) 1994]

(a) >550 cm/sec²
(b) >750 cm/sec²
(c) >950 cm/sec²
(d) >980 cm/sec²

Correct Answer: (d) >980 cm/sec²

Solution:The acceleration due to gravity of a catastrophic earthquake will be greater then 980 cm/sec² or 9.8 m/sec².

23. The mas of the body on the earth is 100kg (acceleration due to gravity of the earth is Ge=10m/s²).if the acceleration due to gravity on the moon is Ge/6 then the mass of the body on the moon is - [I.A.S. (PRE) 2001]

(a) 100/6 kg
(b) 60 kg
(c) 100 kg
(d) 600 kg

Correct Answer: (c) 100 kg

Solution:The mass of the body does not change the with respect to gravity.it is the weight that changes due to increase and decrease in gravity.So the mass of body will remain the same as on the moon as it was on the earth.

24. Weightless is - [M.P.P.C.S.(PRE) 1991]

(a) zero gravity
(b) when gravity decrease
(c) In vacuum
(d) None of the above

Correct Answer: (a) zero gravity

Solution:The phenomena of weightlessness occurs when there is no force to support on your body. when your body is effectively in free fall accelerating downwards at the acceleration of gravity then you are not being supported .Then sensation of the apparent weight comes from the support that you feel from the floor from the seat etc.The term zero gravity is often used to describe such condition.

25. The Earth travels in its orbit at a speed of approx 4,400 km per hour. Why do we not feel this high speed? [U.P.P.C.S.(MAINS) 2013]

(a) Because we are too small compared to the size of the earth.
(b) Our relative speed with respect to the Earth along the earth's orbit is zero.
(c) The solar system as a whole is also moving.
(d) The gravity of the Earth constantly pulls us towards the Earth's centre.

Correct Answer: (b) Our relative speed with respect to the Earth along the earth's orbit is zero.

Solution:The Earth spins and moves through space in an orbit around the sun. We don't 'feel' this movement because we are spinning and moving through space with the Earth. Since we are standing on the Earth, we move as much (and as fast) as the Earth moves. One way to recognize the Earth's movement is to look at objects that are not attached to Earth, like the Sun or stars. For example, if we are in a car which is moving at a constant speed on a smooth surface, we will not feel its motion. However, when the car accelerates or when the brakes are applied, we do feel the motion.

26. If the gravitational force of the earth suddenly disappears which of these will be correct consequence ? [U.P.P.C.S.(MAINS) 2012]

(a) the weight of the object will become zero but the mass of the object remains the same
(b) the mass of the object will become zero but the weight of the object remains the same
(c) both the mass and the weight will become zero
(d) the mass of the object will increase.

Correct Answer: (a) the weight of the object will become zero but the mass of the object remains the same

Solution:if the gravitational force of the earth suddenly disappears then the weight of an object will become zero but the mass will remain same.

27. An artificial satellite orbiting around the earth does not fall down this is so because the attraction of earth - [I.A.S. (PRE) 2011]

(a) does not exist at such a distance
(b) is neutralized by the attraction of the moon
(c) provides the necessary speed for its steady motion
(d) provide the necessary acceleration for its motion

Correct Answer: (d) provide the necessary acceleration for its motion

Solution:An artificial satellite orbiting around the earth does not fall down because the gravitational attraction for its motion in a curved path.

28. Satellite is kept moving in its orbit around the earth it is due to - [U.P.P.C.S.(MAINS) 2013]

(a) centrifugal force
(b) centripetal force
(c) gravitational force or lack of it
(d) some other forces

Correct Answer: (b) centripetal force

Solution:centripetal force is a real force that counteracts the centrifugal force and prevents the objects from flying out keeping it moving instead with uniform speed along the circular or elliptical path .gravity is the centripetal force that keeps planets moving around the sun and the satellites moving around the planets.

29. A geosynchronous satellite continuously active in its orbit due to centripetal force which is obtained by- [U.P.P.C.S.(pre) 2006]

(a) the rocket engine that propelled the satellite
(b) the gravitational force on the satellite by the earth
(c) the gravitational force on the satellite by the sun
(d) the gravitational force on the earth by the satellite

Correct Answer: (b) the gravitational force on the satellite by the earth

30. The known forces of the nature can be divided into four classes viz gravity, electromagnetic, weak nuclear forces, and strong nuclear forces.with the reference to them which on of the following statement is not correct ? [I.A.S. (PRE) 2013]

(a) gravity is the strongest of the four
(b) electromagnetic acts only on the particles with an electric charge
(c) weak nuclear forces causes radioactivity
(d) strong nuclear force holds protons and neutrons inside the nucleus of an atom

Correct Answer: (a) gravity is the strongest of the four

Solution:gravitational forces is the weakest forces among the four fundamental forces while strong nuclear force that holds the position of strongest force among them.

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Motion Under Gravity