MEASUREMENT OF MASS, WEIGHT AND DENSITY · Mass and weight Ans. The quantity of matter in a body is called its mass. It remains constant everywhere and measured in grams and kilograms

1Class-VII Physics Question Bank

1 MEASUREMENT OF MASS, WEIGHT ANDDENSITY

I. Tick (✔✔✔✔✔) the most appropriate answer.1. The SI unit of weight is

(a) kg (b) newton (c) newton-metre (d) km2. We use a beam balance to measure

(a) weight (b) mass (c) force (d) length3. Mass is a

(a) Scalar quantity (b) vector quantity(c) normal quantity (d) none of these

4. The SI unit of density is(a) g/m3 (b) kg/m3 (c) g/cm3 (d) kg/cm3

5. The density of aluminium is 2.7 g/cm3. Its density in kg/m3 is(a) 27 kg/m3 (b) 2700 kg/m3 (c) 270 kg/m3 (d) 27000 kg/m3

6. To determine the density of a solid, we have to determine its(a) mass and area (b) weight and area(c) mass and volume (d) weight and volume

7. When a fluid is heated, it expands and becomes(a) lighter (b) heavier (c) no change (d) none of these

8. In convection currents, heat is transferred upwards(a) horizontally (b) diagonally (c) vertically (d) none of these

9. A body of density 5.34 g/cm3 in water (density 1.0 g/cm3) will(a) float (b) sink (c) rise (d) none of these

10. When a substance is heated its density(a) increases (b) decreases(c) remains same (d) none of these

11. The SI unit of mass is(a) milligram (b) kilogram (c) gram (d) quintal

12. A body weighs 1 kgf at the equator. Its weight at the north pole will be(a) more than 1 kgf (b) less than 1 kgf(c) same as on equator (d) none of these

13. The density of a body is represented by the expression


(a) D = V/M, (b) D= M×V, (c) D = 1/M×V, (d) D = M/V14. The density of wood is 0.65 gcm–3 in CGS system. Its density in SI

system is(a) 65 kgm–3 (b) 6.5 kgcm–3 (c) 650 kgm–3 (d) 0.65 kgm–3

15. When water is heated, it expands and(a) rises upward (b) moves downward(c) remain at the same place (d) none of these

16. When air is cooled, its density(a) increases (b) decreases(c) remains same (d) none of these

Ans. 1. (b) 2. (b) 3. (a) 4. (b) 5. (b) 6. (c)7. (a) 8. (c) 9. (b) 10. (b) 11. (b) 12. (a)

13. (d) 14. (c) 15. (a) 16. (a)

II (A). Fill in the blanks.1. The SI unit of mass is ____________.2. A knob at the baseboard can be used to raise or lower the

____________ of the physical balance.3. A ____________ is used to measure the weight of a body at a

given place.4. The pointer will read ____________ when there is no load on the

pan of the spring balance.5. Equal volumes of water and kerosene have ____________ masses.6. One kilogram of sugar occupies ____________ space than one

kilogram weight of iron.7. The volume of a stone can be determined by displacement method

using a ____________.8. The relative density of a liquid is determined by using a __________.9. The continuous movement of a fluid when heated is called _______.

10. We use a ____________ to test whether the milk is pure or not.Ans. 1. kilogram 2. beam 3. spring balance

4. zero 5. different 6. more7. measuring cylinder 8. relative density bottle9. convection currents 10. lactometer


II (B). Fill in the blank spaces by choosing the correct words from thegiven list.List : zero, 1.04, poles, equator, never, spring, newton, kg, kg/m3,more, unit, 100, less

1. Mass per ____________ volume is called density.2. An iron needle sinks in water as its density is ______ than 1 g/cm3.3. The SI unit of density is____________.4. A body X floats in a liquid Y. The density of body X is __________

than liquid Y.5. The weight is found by __________ balance.6. The unit of mass in SI system is____________ and the unit of

weight in SI system is ____________.7. One Newton is the force by which a mass of __________ g is

attracted towards earth.8. The weight of a body is maximum at ____________ and minimum

at ____________ of the earth.9. The density of milk is 1.04 g/cm3. Therefore, 1 cm3 of milk has a

mass of ____________ g.10. The mass of a body ____________ zero, whereas the weight of a

body can be ____________.Ans. 1. unit 2. more 3. kg/m3

4. less 5. spring 6. kg,newton7. 100 8. Poles, equator 9. 1.04

10. never, zero

III (A). Statements given below are incorrect. Write the correct statements.1. The quantity of matter in a body is called its weight.

Ans. The quantity of matter in a body is called its mass.2. The value of mass varies from place to place.

Ans. The value of weight varies from place to place.3. Physical balance is used to measure the weight of a body.

Ans. Physical balance is used to measure the mass of a body.4. The density of a substance is defined as the weight per unit volume

of that substance.


Ans. The density of a substance is defined as the mass per unit volumeof that substance.

5. Equal masses of iron and common salt have same volume.Ans. Equal masses of iron and common salt have different volume.

6. The density of water is 1 g/cm3 in the SI unit.Ans. The density of water is 1 g/cm3 in CGS system.

7. The SI unit of relative density is g/cm3.Ans. Relative density is the ratio of the density of a substance and the

density of water. It has no unit.8. Multiplying relative density by 100, we get density of the liquid in

kg/m3.Ans. Multiplying relative density by 1000, we get density of the liquid in

kg/m3.9. When an object is placed in a liquid whose density is lower than the

object, the object will float.Ans. When an object is placed in a liquid whose density is lower than the

object, the object will sink.10. SI unit of weight is kilogram force.

Ans. SI unit of weight is newton.11. More is the density of liquid than a solid, more the volume of solid

will submerge in it.Ans. More is the density of liquid than a solid, less the volume of solid

will submerge in it.12. A piece of iron (density 7.6 gcm–3), sinks in mercury (density

13.6 gcm–3).Ans. A piece of iron (density 7.6 gcm–3), floats in mercury (density

13.6 gcm–3).13. Milligram is a multiple of kilogram.

Ans. Milligram is a sub-multiple of kilogram.14. With the rise in temperature of a liquid its density increases.

Ans. With the rise in temperature of a liquid its density decreases.15. A ship loaded fully in sea water, submerge less in river water.

Ans. A ship loaded fully in sea water, submerge more in river water.


III (B). Write ‘true’ or ‘false’ for each statement given below.1. The quantity of matter contained in a body is called mass.2. The multiple of SI unit of mass is milligram.3. The weight of body can be zero.4. Mass of a body changes on the surface of the moon.5. Density of water at 10°C increases when heated to 30°C.6. The unit of density is kgm–3.7. A body having density less than 1 gcm–3 float in water.

Ans. 1. True 2. False 3. True 4. False 5. False6. True 7. True

IV. Find the odd-one out. Give reasons for your choice.1. Beam balance, spring balance, physical balance.

Ans. Spring balance, because it is used to measure the weight of a bodywhile beam balance and physical balance are used to measure themass of a body.

2. g/cm3, kg/m3, g/m3

Ans. g/m3, because it is not a unit of density while g/cm3 and kg/m3 arethe units of density.

3. Scale pan, stirrups, pointer, stopperAns. Stopper, because all other terms are parts of a physical balance.

4. Mass, beam balance, kilogram, spring balanceAns. Spring balance, because SI unit of mass is kilogram and it is

measured by a beam balance therefore, spring balance is odd one.5. Weight, spring balance, newton, kilogram

Ans. Kilogram, because SI unit of weight is newton and it is measuredby a spring balance therefore, kilogram is odd-one.

V. Match the following.1. mass (a) relative density bottle2. weight (b) hydrometer3. relative density (c) physical balance4. purity of milk (d) spring balance

Ans. 1. (c), 2. (d), 3. (a), 4. (b)


VI. Give reasons for the following.1. A jeweller uses only physical balance.

Ans. A jeweller needs an accurate measurement to measure small amountsof gold, gems, etc. therefore he uses only physical balance.

2. The physical balance is enclosed in a glass case.Ans. The physical balance is enclosed in a glass case. So that, air currents

do not disturb the balancing.3. The beam of a physical balance is raised gently by the lever.

Ans. The beam of a physical balance is raised gently by the lever toensure that the pointer swings equally on both sides of the zeromark on the scale.

4. A ship sinks to a greater depth in river water than in sea water.Ans. Because the density of river water is less than the density of sea

water, that is why a ship sinks to a greater depth in river water thanin sea water.

5. The lower end of the hydrometer is filled with mercury or lead.Ans. To keep the hydrometer upright the lower end of the hydrometer is

filled with mercury or lead.

VII. Differentiate between the following.1. Mass and weight

Ans. The quantity of matter in a body is called its mass. It remains constanteverywhere and measured in grams and kilograms.The weight of a body on the earth is equal to the force with whichthe body is attracted towards the earth. It varies from place to placeand measured in newton (N).

2. Beam balance and spring balanceAns. Beam balance is used to measure the mass of an object by

comparing it with a standard mass.Spring balance is used to measure the weight of a body at a givenplace.

3. Density and relative densityAns. The density of a substance is defined as the mass per unit volume

of that substance. The unit of density in SI system is kg/m3.


The relative density of a substance is defined as the ratio of thedensity of the substance to the density of water at 4°C. It has nounit.

VIII. Answer these questions.1. Define density. Write its SI unit.

Ans. The density of a substance is defined as the mass per unit volumeof that substance

Density = Mass

VolumeIn the SI system the unit of density is kg/m3.

2. Define relative density. Why there is no unit of relative density?Ans. The relative density of a substance is defined as the ratio of the

density of the substance to the density of water at 4°C.Since, relative density is the ratio of the density of a substance andthe density of water therefore it has no units.

3. Relative densities of substances A, B, C and D are 0.38, 2.75, 0.85and 1.52 respectively. Which of these substances are(a) heavier than water? (b) lighter than water?

Ans. (a) Heavier than water — B and D.(b) Lighter than water — A and C.

4. Describe a physical balance.Ans. For more accurate measurement of mass we use physical balance.

It consists of a rigid light beam of aluminium or brass. The beam isbalanced at its centre on a knife edge to fulcrum which rests on aflat piece. The flat piece, made of a hard material such as agate orsteel, is fixed on the top of a vertical pillar. Two scale pans of equalmasses are suspended by stirrups and supported on knife edges atthe two ends of the beam.A pointer is attached at the centre of the beam. It moves over ascale fixed at the base of the pillar. The ends of the beam are providedwith screw nuts. By adjusting the position of the nuts, the pointer ismade to swing equally on both sides of the 0-mark on the scale. Aknob at the baseboard can be used to raise or lower the beam. The


baseboard is made horizontal with the levelling screws. The balanceis enclosed in a glass case so that air currents do not disturb thebalancing.

5. How is the mass of an object measured with a physical balance?Ans. Measurement of mass of an object with the physical balance.

(a) The beam is raised gently by the lever to ensure that the pointerswings equally on both sides of the zero mark on the scale.

(b) The beam is now lowered and the given object is placed on theleft-hand pan.

(c) The known weights are placed on the right hand pan with thehelp of forceps.

(d) The standard weights are adjusted till the pointer either remainsat the zero of the scale or swings equally on both sides of thezero mark. In this position, the total mass of weights on theright-hand pan gives the mass of the object.

6. Describe a spring balance.Ans. Spring balance : A spring balance is used to measure the weight of

a body at a given place. It consists of a steel spring enclosed in ametallic case. The body to be weighed is attached to the lower endof the spring balance. A pointer is attached to the lower end of thespring. It rests against the scale graduated on the case.

7. How is the weight of an object measured with a spring balance?Ans. Measurement of weight of an object with a spring balance

(a) We check that when there is no load on the pan the pointerreads zero.

(b) When the body to be weighed is placed on the pan, the springgets elongated due to the weight of the body.

(c) The position of the pointer on the scale thus gives the weight ofthe body.

8. How is the density of a solid (insoluble in water) determined?Ans. Determining the density of a solid. The mass (M) of a stone is

determined by using a physical balance. Its volume (V) is determinedby the displacement method using a measuring cylinder. The


measuring cylinder is half-filled with water and the reading (V1) ofthe water surface is noted. Now, a string is tied to the stone and it isimmersed completely in water. The reading (V2) of the water surfaceis noted. The difference (V2

– V1) gives the volume of the stone.

Now, Density =Mass

Volume = M

V � V2 1

By putting the values of M, V1 and V2, we get the density of thestone.

9. How is the relative density of a liquid measured?Ans. The relative density of a liquid is determined by using a relative

density bottle. It is a small glass bottle. It has a stopper with a finehole. This bottle is used for finding the mass of equal volume ofliquids.

10. How are convection currents formed when a liquid is heated?Ans. When a liquid is heated, it expands and becomes lighter. The hot

liquid (being lighter) rises upwards and carries its heat along withit. The cold liquid (being denser) moves downwards to take theplace vacated by hot liquid. This cold liquid then gets heated andmoves upwards. And more cold liquid moves downwards. Thisprocess of hot liquid moving upwards and cold liquid movingdownwards takes place again and again. These movements of liquidare called convection currents. In this process heat is transferredvertically upwards.

11. What are Plimsoll lines?Ans. Changes in the density of water have serious effects on ships. When

a cargo ship is loaded in a sea port, the captain has to limit the loadit carries, if he is to sail on a river. River water with a lower densitywill cause the ship to sink if it is carrying a heavy load. For safetyconsiderations, all ships have markings on their sides to show thewater level upto which they should be submerged. These markingsare called Plimsoll lines.

12. (a) Define mass (b) State the SI unit of mass (c) Name two multiplesand two submultiples of SI unit of mass.


Ans. (a) The quantity of matter in a body is called its mass.(b) SI unit of mass is kilogram.(c) Two multiples of mass are quintal and tonne

where 1 quintal = 100 kilogramsand 1 tonne = 10 quintals = 1000 kilogramsTwo submultiples of mass are gram and milligramwhere 1000 grams = 1 kilogramand 1000 milligrams = 1 gram

13. (a) Define weight. (b) State and define SI unit of weightAns. (a) The weight of a body on the earth is equal to the force with

which the body is attracted towards the earth. It varies fromplace to place and measured in newtons (N).

(b) The SI unit of weight is newton.The amount of force acting on a body, when the earth pulls amass of 1000 g, is equal to one newton.

14. (a) What do you understand by the term “density” as applied tomatter. (b) State units of density in (i) CGS system (ii) SI system.

Ans. (a) The density of a substance is defined as the mass per unit volumeof that substance

Density =Mass

Volume(b) (i) Unit of density in CGS system is g/cm3.

(ii) Unit of density in SI system is kg/m3.15. The density of lead is 11.6 g/cm3 and that of wood is 800 kg/m3.

What do you understand by these statements.Ans. The density of lead is 11.6 g/cm3 means mass of 1 cm cube of lead

is 11.6 g.The density of wood is 800 kg/m3 means mass of 1 m cube of leadis 800 kg.

16. Briefly describe how will you experimentally find the density ofkerosene oil with the help of a “density bottle”.

Ans. Take a clean and dry relative density bottle and weigh it accuratelyalong with the stopper on a physical balance. Record the mass of


the empty bottle. Let it be M1 grams. Now fill the relative densitybottle with water and insert the stopper. The water fills the hole inthe stopper and some of it overflows. Wipe off the extra water andweigh the bottle. Let the mass of the bottle filled with water be M2grams. Empty the R.D. bottle and dry it with hot air. Refill the bottlewith kerosene and insert the stopper. The kerosene fills the hole inthe stopper and some of it overflows. Wipe off the extra liquid andweigh the bottle. Let its mass filled with kerosene be M3 grams.Observation :

Mass of empty R.D. bottle = M1Mass of empty R.D. bottle + water = M2

Mass of empty R.D. bottle + kerosene = M3Calculation :

Mass of water = M2 – M1Mass of kerosene = M3 – M1

So, relative density of kerosene =M � MM � M

3 1

2 1Therefore,Density of kerosene oil = R.D. of kerosene oil × density of water

17. How does the density of a liquid change with the rise in temperature?Ans. With the rise in temperature of a liquid, the volume increases by

large amount and therefore the density of a substance being theratio of mass to its volume decreases considerably.

18. Two solids A and B of density 25 g/cm3 and 0.80 g/cm3 are placedin a liquid L of density 1.2 g/cm3. Which solids is likely to float andwhy?

Ans. Those substance whose density is less than the density of a liquidwill float in the liquid. Since the density of solid B is 0.80 g/cm3

which is less than the density of the liquid 1.2 g/cm3 will float.19. Why do the bodies like stone and metals sink in water?

Ans. Because the density of the bodies like stone and metals is morethan the density of water, hence, they sink in water.

20. Why do the bodies like cork and wood float in water?


Ans. Because the density of the bodies like cork and wood is less thanthe density of water, hence, they float in water.

21. Why does an iron needle sink in water, but an iron ship float inwater?

Ans. Iron needle is compact and its density is 7.6 g/cm3 which is morethan the density of water 1g/cm3, therefore, it sinks in water.However, the iron ship which is constructed in such a way that it ismostly hollow from within. Thus, the volume of iron ship becomesvery large as compared to its mass, and hence, its density is lessthan 1 g/cm3. As the density of iron ship is less than 1 g/cm3 therefore,it floats in water.

IX. Practice for numerical problems.1. A piece of wood of mass 160 g has a volume of 200 cm3. Find the

density of wood in the (a) CGS system (b) SI system.Ans. Mass of wood (M) = 1600 g

Volume of wood (V) = 200 cm3

(a) Density of wood (D) in CGS system

=MV =

160200 g/cm3

= 0.8 g/cm3

(b) Density of wood (D) in SI system= 1000 × 0.8= 800 kg/m3

2. A block of metal of dimensions 4 cm, 5 cm and 25 cm has a massof 1.280 kg. Find the density of the block in kg/m3.

Ans. Mass of metal (M) = 1.280 kgVolume of metal (V) = 4 cm × 5 cm × 25 cm

= 500 cm3 = 0.0005 m3

∴ Density of metal (D) =MV =

1.2800.0005 kg/m3

= 2560 kg/m3


3. Calculate the volume of wood of mass 200 kg when the density ofwood is 800 kg/m3.

Ans. Mass of wood (M) = 200 kgDensity of wood (D) = 800 kg/m3

∴ Volume of wood (V) =Mass of wood ( )

Density of wood ( )M

D

=200800 m3 = 0.25 m3

4. The volume of a metal cube is 125 cm3. If the density of the metal is13.6 g/cm3, find the mass of the metal in kilograms.

Ans. Volume of metal cube (V) = 125 cm3

Density of metal (D) = 13.6 g/cm3

∴ Mass of the metal (M) = V × D = 125 cm3 × 13.6 g/cm3

= 1700 g = 1.7 kg5. An empty relative density bottle weighs 23.4 g. When fully filled

with water, its weight is 46.8 g. When filled with a liquid, its weightis 52.4 g. Find the relative density of the liquid.

Ans. Mass of empty R.D. bottle M1 = 23.4 gMass of R.D. bottle + water M2 = 46.8 gMass of R.D. bottle + liquid M3 = 52.4 g

Now, mass of water = M2 – M1 = 46.8 g – 23.4 g = 23.4 gAnd, mass of liquid = M3 – M1 = 52.4 g – 23.4 g = 29 g

So, relative density of the liquid =M � MM � M

3 1

2 1 =

29 g23.4 g = 1.24

6. Find the relative density of a liquid from the following observations.(a) Mass of empty R.D. bottle = 25.2 g(b) Mass of empty R.D. bottle + water = 57.7 g(c) Mass of empty R. D. bottle + liquid = 52.7 g

Ans. We have,Mass of empty R.D. bottle = 25.2 g

Mass of empty R.D. bottle + water = 57.7 g


Mass of empty R.D. bottle + liquid = 52.7 gNow, mass of the water = 57.7 g – 25.2 g = 32.5 gAnd, mass of the liquid = 52.7 g – 25.2 g = 27.5 g

Therefore, relative density of the liquid = Mass of the liquidMass of the water

=27.5 g32.5 g

= 0.8467. Calculate the density of a solid from the following data.

(a) mass of solid = 75.8 g(b) initial volume of water in measuring cylinder = 24 cm3.(c) final volume of water + solid in measuring cylinder = 42 cm3

Ans. We have,Mass of solid = 75.8 g

Initial volume of water in measuring cylinder = 24 cm3

Final volume of water + soild in measuring cylinder = 42 cm3

So, volume of solid = 42 cm3 – 24 cm3 = 18 cm3

Therefore, density of soild = Mass of solid

Volume of solid = 75.8 g18 cm3

= 4.21 g/cm3

8. (a) Density of aluminium is 2.7 g/cm3. Express the density inkg/m3.

(b) Density of alcohol is 800 kg/m3. Express the density in g/cm3.Ans. (a) Density of aluminium = 2.7 g/cm3

Density of aluminium in kg/m3 = 1000 × 2.7 kg/m3

= 2700 kg/m3

(b) Density of alcohol = 800 kg/m3

Density of alcohol in g/cm3 =800

1000 g/cm3 = 0.80 g/cm3

9. 5 litres of kerosene oil is found to weigh 4.40 kg. Find the density ofkerosene oil in (a) CGS system and (b) SI system.


Ans. Mass of kerosene oil (M)= 4.40 kgVolume of kerosene oil (V) = 5 litre = 5000 cm3

(a) Density of kerosene oil (D) in CGS system

=MV =

4.40 � 1000 g5000 cm 3

= 0.88 g/cm3

(b) Density of kerosene oil (D) in SI system

=MV =

4 403

. kg5000

100 �100 �100m

=4.40 kg

0.005 m 3 = 880 kg/m3

10. Calculate the density of solid from the following data:(a) Mass of solid = 72 g(b) Initial volume of water in measuring cylinder = 24 cm3

(c) Final volume of water when solid is immersed in water = 42 cm3.Ans. We have,

Mass of solid = 72 gInitial volume of water in measuring cylinder = 24 cm3

Final volume of water + soild in measuring cylinder = 42 cm3

So, volume of solid = 42 cm3 – 24 cm3 = 18 cm3

Therefore, density of soild = Mass of solid

Volume of solid = 72 g

18 cm 3

= 4 g/cm3

11. An empty density bottle weighs 22 g. When completely filled withwater it weighs 50 g and when completely filled with brine solution itweighs 54 g. Calculate (a) volume of density bottle (b) density ofbrine solution.

Ans. Mass of empty density bottle = 22 gMass of empty density bottle + water = 50 g


Mass of empty density bottle + brine solution = 54 g(a) Mass of water in density bottle = 50 g – 22 g = 28 g∴ Volume of 1 g water = 1 cm3

∴ Volume of 28 g water = 28 cm3

So, volume of density bottle = 28 cm3

(b) Mass of brine solution in density bottle = 54 g – 22 g = 32 gTherefore, relative density of brine solution

= Mass of brine solution

Mass of water = 32 g28 g = 1.14

Hence, Density of brine solution = Relative density of brine solution× density of water

= 1.14 × 1 g/cm3 = 1.14 g/cm3

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MEASUREMENT OF MASS, WEIGHT AND DENSITY · Mass and weight Ans. The quantity of matter in a body is called its mass. It remains constant everywhere and measured in grams and kilograms