Answer: Option B. -> False
:
B
Gravitational force is independent of the medium between the two bodies. Hence, the gravitational force between the Earth and its moon would remain the same irrespective of the medium between the two.

Answer: Option C. -> Spring-balance
:
C
Spring balance or spring scale measures weight (force) by balancing the force due to gravity against the force of an extended spring.

Answer: Option A. -> Mass is constant and weight is variable.
:
A
Mass of abody is the amount of matter present in thebody whereas weight is the magnitude of gravitational force acting on the body. Mass of an object remains constant. Weight of the body varies with 'acceleration due to gravity' because it depends on other parameters.

Answer: Option D. -> Unitless
:
D
Relative density of a substance is a pure ratio of density of the substance to the density of water. Hence, relative density has no unit.

Answer: Option A. -> Density
:
A
Densityis a measurement that compares the amount of matter an object has to its volume. An object with much matter in a certain volume has highdensity. An object with little matter in the same amount of volume has a lowdensity.Densityis found by dividing the mass of an object by its volume.

Answer: Option A. -> The force acting between two objects are in the same direction but with different magnitudes.
:
A
Gravitationor gravity is a natural phenomenon by which all physical bodies attract each other. Any object with a mass will experience a gravitational force. Since it is attractive in nature, it always tries to pull the objects towards each other.
The direction of arrow D represents the gravitational force acting on A due to B. Similarly, the direction of arrow C represents the gravitational force acting on B due to A. The magnitude of the force acting on each other is equal, only the direction differs.

Answer: Option B. -> 3.335×10−9 N
:
B
Given, mass of first body, $m_1=50kg$ and mass of second body, $m_2=100kg$
Distance between the two masses is, $r=10m$.
According to Universal law of gravitation, force of attraction between two bodies is
$F=\frac{G{m}_1{m}_2}{r^2}$
where, $G$ is the gravitational constant and $G=6.67\times {10}^{-11}N{m}^{2}k{g}^{-2}$
$\therefore$ $F=\frac{6.67\times {10}^{-11}\times 50\times 100}{{10}^2}$
$\Rightarrow$ $F=33.35\times {10}^{-10}$ N
$\Rightarrow$ $F=3.335\times {10}^{-9}$ N

Answer: Option B. -> zero
:
B
Weight of a body is given by:
$W=mg$
where:
$m:$ Mass of the body
$g:$ Acceleration due to gravity
At the center of earth, acceleration due to gravity is zero. This is because mass of earth is distributed uniformly about this point. For every small part of mass of earth that attracts the body in one direction, we can find another small mass that will attract it in opposite direction with the same force. The net force due to each such pair is zero.
Hence, net force at the center of earth is zero.

Answer: Option A. -> 32 N
:
A
Weight of the body at earth's surface is:
$W_e=\frac{GMm}{R^2}$ .......(1)
where, G-universal gravitational constant, M-mass of earth and R-radius of earth, m- Mass of the body
Weight of the body at a height $h$ above the earth's surface is given by
$W_e^{\prime }=\frac{GMm}{{(R+h)}^2}$
According to the question, $h=\frac{R}{2}$
$W_e^{\prime }=\frac{GMm}{{(R+\frac{R}{2})}^2}$
$W_e^{\prime }=\frac{4GMm}{9R^2}$....(2)
Dividing equation (2) by equation(1), we get
$\frac{W_e^{\prime }}{W_e}=\frac{4GMm/9R^2}{GMm/R^2}$
$\frac{W_e^{\prime }}{W_e}=\frac{4}{9}$
Given weight on earth's surface is, $W_e=72N$
$\frac{W_e^{\prime }}{72}=\frac{4}{9}$
$W_e=32N$

Answer: Option A. -> 10 ms−1
:
A
Any body in free fall is under acceleration due to gravity (g) and thus accelerates at $9.8m{s}^{-2}$. When a body starts from rest, after one second it will gain an acceleration of$9.8m{s}^{-2}$ and thus will be at a velocity of$9.8m{s}^{-1}$ in the downward direction. When rounded off to the nearest integer, the answer becomes 10.