6 The International System of Units Unit Prefixes – Problems and Solutions
The International System of Units
1. Which of the following units is not a unit of length
A. Mil
B. Foot
C. Inch
D. Knot
Solution :
Mil, foot, and inch are units of length.
The knot is a unit of velocity or speed.
The correct answer is D.
2. Determine the unit of the international system of Young’s modulus
A. kg.m/s2
B. kg/m.s2
C. m/kg.s2
D. kg.s2/m
Known :
Unit of force = kg m/s2
Unit of area = m2
Unit of length = m
Wanted: The unit of the international system of Young‘s modulus.
Solution :
The correct answer is B.
3. Quantity has unit kg.m-1.s-2 is…
A. Pressure
B. Energy
C. Momentum
D. Acceleration
Solution :
Pressure = Force / Area
The international unit of force is kg m/s2
The international unit of area is m2
The international unit of pressure = kg /m s2 = kg m-1 s-2
Energy = Work
Work = Force x Displacement
The international unit of force is kilogram meter per second squared (kg m/s2)
The international unit of displacement is a meter (m)
So, the international unit of energy = unit of work = kg m2/s2 = kg m2 s-2
Momentum = Mass x velocity
The international unit of mass is kg
The international unit of velocity is m/s
So, the international unit of momentum is kg m/s = kg m s-1
Acceleration = velocity / time interval
The international unit of velocity is meter/second (m/s)
The international unit of time is second (s)
Therefore, the international unit of acceleration is m/s : s = m/s x 1/s = m/s2 = m s-2
The correct answer is A.
4. The international unit of power is…
A. kg m2 s-2
B. kg m2 s-3
C. g cm2 s-1
D. g cm s-3
Solution :
Power = Work / time
The international unit of work is kilogram meter squared per second squared (kg m2/s2)
The international unit of time is second (s)
So, the unit of power is kg m2/s3 = kg m2 s-3
The correct answer is B.
Unit Prefixes
5. The order of prefix for units from big to small that correct is…
A. Mega, tera, nano, pico
B. Giga, Mega, Micro, nano
C. Pico, Nano, Mega, Tera
D. Mega, Tera, Micro, Pico
Solution :
The correct answer is B.
6. A micro century is the same as ….
A. 1 hour
B. 90 minutes
C. 52 minutes
D. 4000 seconds
Known :
1 day = 24 hours
1 hour = 60 minutes
1 minutes = 60 seconds
1 day = 24 x 60 minutes = 1440 minutes
1 day= 1440 x 60 seconds = 86,400 seconds
Wanted : 1 micro century = ….. hours = ….. minutes = ….. seconds
Solution :
1 micro = 10-6
1 micro century = 10-6 century = 0.000,001 centuries
1 century = 100 years = 100 x 365 years= 36,500 years
1 micro century = 0.000,001 x 36,500 days = 0.0365 days
1 micro century = 0.0365 x 24 hours = 0.876 hours
1 micro century = 0.876 x 60 minutes = 52.56 minutes
1 micro century = 52.56 x 60 seconds = 3153.6 seconds
The correct answer is C.