 # Quantities and units of physics – problems and solutions

1. The correct International Unit showed by student…

A. R and S

B. P and R

C. P and Q

D. Q and S

Solution

Student P :

The international unit of length is meter (m), not centimeter (cm)

The measuring instrument of length is the ruler.

Student Q :

The international unit of electric current is Ampere (A)

The measuring instrument of electric current is an Ampere meter.

Student R :

The international unit of temperature is Kelvin (K)

The measuring instrument of temperature is a thermometer, not a hydrometer.

A hydrometer is an instrument used for measuring the density of liquids based on the concept of buoyancy.

Student S :

The international unit (SI) of mass is kilogram (Kg)

The measuring instrument of mass is a balance scale

The correct data and based on the SI unit (International Unit) shown by student Q and S.

2. Find the correct relation between quantity and unit. Solution

Force = Mass x Acceleration

The international unit of mass is kilogram (kg)

The international unit of acceleration is meter per second squared (m/s2)

Unit of force = kg m/s2 = kg m s-2

Pressure = force / area

International unit of force is kg m/s2

The international unit of area is m2

Unit of pressure = kg /m s2 = kg m-1 s-2

Energy = Work

Work = force x displacement

International unit of force is kilogram meter per second squared (kg m/s2)

The international unit of displacement is meter (m)

Unit of energy = unit of work= kg m2/s2 = kg m2 s-2

Power = Work / time

International unit of work is kilogram meter squared per second squared (kg m2/s2)

The international unit of time is second (s)

Unit of power is kg m2/s3 = kg m2 s-3

3. Based on the above table, find A, B, C, D, and E.

A. Volume, kilogram, temperature, area, meter

B. Length, kilogram, time, area, Newton

C. Length, kilogram, volume, area, Joule

D. Length, Newton, time, volume, meter

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Solution :

A = Length

B = Kilogram

C = Time

D = Area

E = Kg m/s2 = Newton

4. Determine the pair of basic quantities and units in the International System.

A. Length– meter, mass – kg and electric charge—coulomb

B. Time – second, temperature – Kelvin, luminous intensity—Candela

C. Second – time, meter – length, kg—mass

D. mass – kg, time– second, Kelvin – temperature

Solution

Basic quantities and International unit (SI) :

Length – meter (m)

Mass – kilogram (kg)

Time – second (s)

Temperature – Kelvin (K)

Luminous intensity—Candela

5. The correct quantities and units based on the International System of Units (SI) shown by number…

A. 1 and 3

B. 1 and 4

C. 1, 2, and 3

D. 1, 3, and 4

Solution

Quantities and units of the International System (SI) :

(1) Temperature – Kelvin

(2) Mass – Kilogram

(3) Time – Second

(4) Length – Meter