Test: Archimedes Principle (Old Syllabus) - Class 9 MCQ

The buoyant force experienced by the object is:- The buoyant force is in opposite direction to the weight of the object. Hence, if the object weighs 4.5 N in liquid then 0.5 N buoyant force will act on the object.

The density of liquid B is more than the liquid A as more upthrust is exerted on the body in liquid B and hence it sinks less.

• When the body is completely immersed in the liquid: This is when the maximum apparent loss in weight of the body will be observed. When the body is completely immersed in the liquid, the weight of the displaced liquid is equal to the weight of the body. This results in the maximum apparent loss in weight.


• When the body just touches the surface of the liquid: At this point, the apparent loss in weight will not be at its maximum as the body has not displaced enough liquid to equal its weight.


• When the body is partially immersed and also touches the sides of the container: This scenario will not result in the maximum apparent loss in weight as the body is not completely submerged in the liquid.


• When the body is partially immersed in the liquid: Similar to when the body touches the sides of the container, this scenario will not result in the maximum apparent loss in weight as the body is not completely submerged in the liquid.

Density of copper = 9 gm/cm^3
Mass of copper  =  90 g
We know;  Density =  mass / volume
⇒ volume  = mass / density
⇒    90 / 9
⇒ Volume  = 10 cm³

Density is defined as the mass per unit volume. In seawater, the salts are dissolved in water resulting in an increase in their mass per unit volume. Hence, seawater is denser than freshwater because of the dissolved salts in seawater, its density increases.

• Definition: A hydrometer is an instrument used to measure the density or relative density of liquids.



• Working Principle: Hydrometers work on the principle of buoyancy. The density of a liquid affects the buoyancy force acting on the hydrometer, causing it to float at different levels in liquids of different densities.



• Construction: A typical hydrometer consists of a weighted glass tube with a scale inside. The scale is calibrated to read the density or specific gravity of the liquid being measured.



• Usage: Hydrometers are commonly used in various industries such as the food and beverage industry, chemical industry, and pharmaceutical industry to measure the density of liquids accurately.



• Types: There are different types of hydrometers available for specific applications, such as alcohol hydrometers for measuring alcohol content in beverages or battery hydrometers for measuring the specific gravity of battery acid.

• Volume of packet: 200 cm³


• Mass of packet: 400 g


• Density formula: Density = Mass/Volume


• Substitute values: Density = 400g / 200cm³ = 2 g/cm³


• Relative density formula: Relative density = Density of substance / Density of water


• Considering density of water: 1 g/cm³


• Substitute values: Relative density = 2 g/cm³ / 1 g/cm³ = 2

• Relative density is the ratio of the density of a substance to the density of a reference substance.


• Relative density is a dimensionless quantity.


• Given relative density = 11.3

• The density of a substance is calculated by multiplying the relative density by the density of the reference substance.


• The density of water at 4 degrees Celsius is 1000 kg/m^3.


• So, density of the substance = Relative density x Density of water = 11.3 x 1000 kg/m^3 = 11300 kg/m^3

• The density of the substance in SI units is 11.3 x 10^3 kg/m^3

If the density of the object placed in liquid is equal to the density of the liquid, then :- It would float submerged in the liquid. Some part of the solid would be above the liquid surface and part would be inside the liquid surface.

• Density of Object A: 1.12 g cm^-3


• Density of Object B: 0.92 g cm^-3


• Density of Object C: 2.02 g cm^-3

• When an object is placed in water, it will float if its density is less than the density of water (1 g/cm³).


• Object A has a density of 1.12 g/cm³, which is greater than the density of water.


• Object B has a density of 0.92 g/cm³, which is less than the density of water.


• Object C has a density of 2.02 g/cm³, which is greater than the density of water.


• Therefore, Object A and Object C will sink in the water tank, while Object B will float.

• Object A and Object C will sink in the water tank.


• Object B will float in the water tank.


• Hence, the correct answer is A and C.