Free Gravitation MCQs with Answers

1. A guy is standing in a lift falling freely under gravity and releases a ball from his hand. As seen by the ball, the boy:

• A. Falls down
• B. Remains stationary
• C. Goes up
• D. None of above

Explanation: The acceleration of the body does not depend on the mass (for freely falling). Hence both boy and ball have same acceleration. Hence their velocities at every point would be same. So "Relative" velocity is 0. Hence the boy will remain stationary as seen by the ball.

2. Two spheres of the same size, one of mass 5 kg and the other of mass 50 g are dropped simultaneously from a tower. When they are about to touch the ground, they have the same:

• A. Kinetic Energy
• B. Potential Energy
• C. Momentum
• D. Acceleration
• E. All given options

Explanation: KE, PE and momentum will be different because they depend on mass. The acceleration of the object is independent tof mass rather only dependent on the gravitational field strength which is same for both.

3. The radius of the moon is 27% off the earth's radius and its mass is 1.2% of the earth's mass. Find the acceleration due to gravity on the surface of the moon:

• A. 0.431 m/s2
• B. 1.615 m/s2
• C. 2.431 m/s2
• D. 3.615 m/s2
• E. 4.431 m/s2

Explanation: Let M & M' be the mass of earth & moon. Also R & R' be their radius respectively. Given is - M' = 1.2% M = 0.012 M R' = 27% R = 0.27 R Gravitationalacceleration on earth's surface is - g = GM / R2 Gravitationalacceleration on supposed planet is - g' = GM' / R'2 g' = G(0.012M) /(0.27R)2 g' = (0.012/0.272)GM/R^2 g' = 0.1646 g g' = 0.1646 × 9.8 g' = 1.613 m/s2 Therefore, acceleration due to gravity on the moon's surface is 1.613 m/s2.

4. S.I. Unit of universal gravitational constant G is:

• A. Nm2/kg
• B. Nm2/kg2
• C. Nm/kg2
• D. Nm/kg

Explanation: Force =GM1M2\R2 [G]=[Force][R2]\[M1][M2] G=Nm2/(kg)2 G= Nm2/kg2

5. Artificial gravity can be supplied by which of the following ways so that normal force of gravity can be generated for the astronaut:

• A. Rotating the space craft
• B. Back and forth motion spacecraft
• C. Up and down movement of spacecraft
• D. Keeping the space craft stationary
• E. All of the above

Explanation: In space, it is possible to create "artificial gravity" by spinning your spacecraft or space station. Technically, rotation produces the same effect as gravity because it produces a force (called the centrifugal force) just like gravity produces a force.

6. The mass of earth on the basis of Newton's Law of Gravitation is given by:

• A. M = 9.1 x 10^-31 kg
• B. M = 1.6027 x 10^-27 kg
• C. M = 5.98 x 10^24 kg
• D. M = 6.02 x 10^23 kg
• E. M = 3 x 10^3 kg

Explanation: By equating Newton's second law with his law of universal gravitation, and inputting for the acceleration the experimentally verified value of 9.8 m/s2, the mass of the earth is calculated to be 5.98 x 10^24 kg . Since it is numerically derivated so it could have only one answer.

7. If the diameter of the earth becomes two times its present value and its mass remains unchanged, then how would the weight of an object on the surface of the earth be affected?

• A. Becomes double
• B. Becomes one fourth
• C. Becomes one third
• D. Remains same
• E. Becomes half

Explanation: Let M be the mass of earth and R be the radius, we know, g=GM/R2 so, if diameter is doubled i.e. d' = 2d which means R' = d = 2R ⇒ g' = GM/4R2 = g/4 So g becomes g/4. Also Weight=Mass of the object W'=(mass of object*g)/4 That is, the weight becomes 1/4.

8. When a body moves in the direction of gravitational force i.e. towards the earth, the work is done by the force of gravity on the body and is _, whereas when the body moves against the direction of gravitational force, the corresponding work done is _.

• A. negative, positive
• B. positive, negative
• C. positive, positive
• D. negative, negative
• E. Insufficient Information

Explanation: When the work is done in the direction of the force then work done is said to be positive. However, if the work is in opposition to the direction of force then the work done is said to be negative.

9. A solar day is the time interval between two successive appearances of the sun overhead. The time that is referred to the rotation of the earth about its axis is called:

• A. Universal Time
• B. Length of the day
• C. Time interval
• D. Solar day

Explanation: A solar day is time lnterval between two successlve appearance of the sun overhead. Thus mean second, representing the basic unit of time, was originally defned as (1/60) (1/60) (1/24) of a mean solar day. The tme that is referred to rotation of the earth about its axis is called universal time. STB-Chapter#1.

10. Find the gravitational force of attraction between two balls each weighing 10 kg, when placed at a distance of 1 meter apart.

• A. 6.673 x 10^-9 N
• B. 7.71 x 10^-9 N
• C. 8.91 x 10^-9 N
• D. 9.91 x 10^-9 N
• E. 10.31 x 10^-9 N

Explanation: F = (G * m1 * m2) / r2 where F is the gravitational force, G is the gravitationalconstant (approximately 6.674 × 10-11 N m2/kg2), m1 and m2 are the masses ofthe objects and r is the distance between their centers. Given that both balls weigh 10 kg and are placed 1 meter apart,we can substitute the values into the formula: F = (6.674 × 10-11 N m2/kg2 * 10 kg * 10 kg) / (1 m)2 F = (6.674 × 10-11 N m2/kg2 * 100 kg2) / 1 m2 F = 6.674 × 10-9 N Therefore, the gravitational force of attraction between thetwo balls weighing 10 kg each, when placed 1 meter apart, is approximately6.674 × 10-9 Newtons.