Online Test: Gravitation | Class 9 Physics

Question 1 of 20

In $F = \dfrac{G m_1 m_2}{r^2}$, the force is inversely proportional to:

the distance $r$

the product of masses

the cube of the distance

the square of the distance $r^2$

Explanation: Gravitation follows the inverse-square law, $F \propto 1/r^2$.

Question 2 of 20

The value of the universal gravitational constant $G$ is approximately:

$6.67 \times 10^{-11}\ \text{N m}^2/\text{kg}^2$

$9.8\ \text{N/kg}$

$6.4 \times 10^{6}\ \text{m}$

$1000\ \text{kg/m}^3$

Explanation: $G = 6.674 \times 10^{-11}\ \text{N m}^2/\text{kg}^2$.

Question 3 of 20

Acceleration due to gravity $g$ at Earth's surface is given by:

$g = GMR^2$

$g = \dfrac{GM}{R^2}$

$g = \dfrac{R^2}{GM}$

$g = \dfrac{GM}{R}$

Explanation: Equating $mg = GMm/R^2$ gives $g = GM/R^2$.

Question 4 of 20

If the distance between two masses is tripled, the gravitational force becomes:

3 times

1/3

1/9

9 times

Explanation: $F \propto 1/r^2$, so tripling $r$ gives $1/9$ of the force.

Question 5 of 20

During free fall, all objects (ignoring air) fall with the same:

mass

weight

acceleration $g$

momentum

Explanation: $g$ is independent of mass, so all objects accelerate equally.

Question 6 of 20

A stone dropped from rest has velocity after $3\ \text{s}$ (take $g = 10\ \text{m/s}^2$):

$10\ \text{m/s}$

$20\ \text{m/s}$

$30\ \text{m/s}$

$45\ \text{m/s}$

Explanation: $v = u + gt = 0 + 10 \times 3 = 30\ \text{m/s}$.

Question 7 of 20

A ball is dropped from rest; the distance fallen in $2\ \text{s}$ is (take $g = 10\ \text{m/s}^2$):

$10\ \text{m}$

$20\ \text{m}$

$40\ \text{m}$

$5\ \text{m}$

Explanation: $h = \tfrac12 g t^2 = \tfrac12(10)(4) = 20\ \text{m}$.

Question 8 of 20

Which quantity is the same on the Earth and the Moon?

weight

mass

value of $g$

buoyant force

Explanation: Mass is constant; weight changes with $g$.

Question 9 of 20

The weight of a body is:

$\dfrac{m}{g}$

$\dfrac{g}{m}$

$m + g$

$mg$

Explanation: Weight is the gravitational force, $W = mg$.

Question 10 of 20

On the Moon, an object's weight is about ___ of its Earth weight:

the same

twice

one-sixth

six times

Explanation: Moon's $g$ is about $1/6$ of Earth's.

Question 11 of 20

The SI unit of weight is the:

kilogram

newton

pascal

joule

Explanation: Weight is a force, measured in newtons.

Question 12 of 20

Pressure is defined as:

force $\times$ area

$\dfrac{\text{force}}{\text{area}}$

$\dfrac{\text{area}}{\text{force}}$

mass $\times$ area

Explanation: $P = \dfrac{F}{A}$.

Question 13 of 20

The SI unit of pressure is the:

newton

pascal

watt

joule

Explanation: $1\ \text{Pa} = 1\ \text{N/m}^2$.

Question 14 of 20

A force of $100\ \text{N}$ on an area of $5\ \text{m}^2$ gives a pressure of:

$20\ \text{Pa}$

$500\ \text{Pa}$

$5\ \text{Pa}$

$105\ \text{Pa}$

Explanation: $P = 100/5 = 20\ \text{Pa}$.

Question 15 of 20

A sharp knife cuts better than a blunt one because it:

increases the force

decreases the area, raising pressure

increases the area

lowers the pressure

Explanation: Smaller area means larger pressure for the same force.

Question 16 of 20

Archimedes' principle states the upthrust equals the:

weight of the body

weight of fluid displaced

volume of the body

density of the fluid

Explanation: Upthrust = weight of fluid displaced.

Question 17 of 20

An object floats in water if its density is:

greater than water's

less than water's

equal to its mass

equal to its volume

Explanation: Lower density than the fluid means it floats.

Question 18 of 20

Relative density is the ratio of a substance's density to that of:

air

mercury

water

oil

Explanation: R.D. $= \rho_{substance}/\rho_{water}$ and has no units.

Question 19 of 20

Fluid pressure ___ as depth increases.

decreases

stays constant

becomes zero

increases

Explanation: Deeper fluid columns press harder, so pressure increases with depth.

Question 20 of 20

An object weighs $40\ \text{N}$ in air and $35\ \text{N}$ in water. The buoyant force is:

$5\ \text{N}$

$35\ \text{N}$

$40\ \text{N}$

$75\ \text{N}$

Explanation: Apparent loss in weight $= 40 - 35 = 5\ \text{N}$ is the upthrust.

Online Test — Gravitation