Free Gravitation MCQs with Answers

221. A monkey sits on the pan of a spring scale. The reading of the spring scale will be maximum when the elevator is kept in an elevator

• A. is stationary
• B. accelerate downward
• C. Cable brakes and it falls freely towards the earth
• D. accelerates upward

Explanation: The reading of the spring scale will be maximum when the elevator accelerates downwards. This is because the apparent weight of the monkey is the sum of its actual weight and the force due to the acceleration, and the apparent weight is maximum when the elevator accelerates downward

222. If the weight of a man is 100N and he is sitting in an elevator. Which is moving down with an acceleration of 9.8 m/s², then the apparent weight of the mass will be

• A. 100 N
• B. 1960 N
• C. 200 N
• D. Zero

Explanation: The apparent weight of an object in an elevator is given by the formula W′=W−ma, where ′W′ is the apparent weight, W is the actual weight, m is the mass of the object, and a is the acceleration. In this case, the elevator is moving downward, so a is positive. Plugging in the values, W′=100N−((100/9.8)×9.8m/s2)=0 N.

223. A body of mass m is attached to a spring balance which is attached to the ceiling of an elevator. If the elevator moves up with a certain acceleration, the apparent weight of the body will be

• A. m(g+a)
• B. g(m+ma/g )
• C. a(m+mg/a )
• D. All of these

Explanation: The apparent weight of the body in an elevator depends on the acceleration of the elevator and the gravitational acceleration.Upward acceleration: The apparent weight is m(g + a).Downward acceleration: The apparent weight is m(g - a).

224. Once the space shuttle is in orbit at a radius R from earth's center, what force does the seat exert on the astronaut?

• A. Mg
• B. Zero newton
• C. M/g
• D. Ng/R2

Explanation: In an orbiting space shuttle, the astronaut is in free fall along with the shuttle, experiencing a gravitational force that provides the necessary centripetal force for the circular orbit. The force exerted by the seat on the astronaut is the normal force, and it is what prevents the astronaut from falling through the seat.The gravitational force acting on the astronaut is given by Fgravity =GMm/R2 The centripetal force required for the circular orbit is given by Fcentripetal =mv2 /RIn a stable orbit, Fgravity and Fcentripetal are equal. The normal force exerted by the seat on the astronaut is also equal to Fgravity , as it needs to counteract gravity to keep the astronaut in place.So, Fgravity =Mg, where g is the acceleration due to gravity at the surface of the Earth.

225. In an artificial satellite, an object appears to be weightless when its rotational acceleration 'α' isequal to

• A. g / 4.
• B. g / 2.
• C. g.
• D. 2 g.

Explanation: In an artificial satellite, an object appears weightless when it is in a state of continuous free fall towards Earth. This happens because the satellite and everything inside it, including the object, are accelerating towards the Earth at the same rate as the gravitational pull, g. Therefore, the correct rotational acceleration, α, that results in weightlessness is equal to g. Other values like g/4, g/2, or 2g do not satisfy the condition for weightlessness, as they do not match the gravitational acceleration.

226. Which of the following is a property of a uniform gravitational field?

• A. Its magnitude is the same in all directions
• B. The gravitational potential has the same value at all points within it
• C. Its direction is opposite to the direction of motion of attest mass released in it
• D. Its field strength is the same at all points within it

Explanation: d) Its field strength is the same at all points within it:This option suggests that the field strength (magnitude of the gravitational field) is the same at all points within a uniform gravitational field. This is correct. In a uniform gravitational field, the field strength is constant throughout the field. The field strength determines the magnitude of the gravitational force experienced by an object in the field.

227. If by some phenomenon the Earth contracts to one half of its present size, then the value of gravitational potential energy becomes:

• A. Double
• B. One-half
• C. Remains the same
• D. Four times

Explanation: The formula for gravitational potential energy is U = -GMm/r Hence, U = 1/r. If r/2, then U = 1/(r/2). Therefore U = 2(1/r), the gravitational potential energy is doubled.

228. The SI unit of gravitational potential is :

• A. J/kg
• B. J/(m kg)
• C. J/(m s)
• D. Js

Explanation: The amount of work required to transport a body of unit mass from infinity to some point is known as gravitational potential. The mathematical expression will be G = W/m. The unit of work is joule and the unit of mass is the kilogram (kg), so the unit of gravitation potential will be J/Kg.

229. Choose the correct option.

• A. Newton discovered that gravity pulled everything away from it.
• B. None of these is correct.
• C. Both of these are correct
• D. Newton discovered that gravity pulls everything towards it.

Explanation: Gravity pulls everything towards it - this is a universal truth. Universal truths are always expressed in the present tense even when narration is in the past. Therefore, the correct sentence is "Newton discovered that gravity pulls everything towards it."

230. The atmosphere around the earth is held by:

• A. Clouds
• B. Winds
• C. Gravity
• D. None of these options are correct

Explanation: The atmosphere around the earth is held by gravitational force or gravity due to the earth. The earth's gravity attracts the atmosphere and keeps it bound. Hence, C is the correct option.