Mathematics
Grade 9
15 min
Relate time units
Relate time units
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1
Introduction & Learning Objectives
Learning Objectives
Convert between standard units of time (seconds, minutes, hours, days, years).
Construct and apply conversion factors to solve multi-step time conversion problems.
Use dimensional analysis to verify the correctness of a unit conversion.
Convert rates involving time units (e.g., kilometers per hour to meters per second).
Express time given as an algebraic expression in different units.
Analyze and solve word problems that require relating different units of time.
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This tutorial will teach you the powerful technique of dimensional analysis to confidently relate and convert any unit of time. This skill is a crucial foundation for solv...
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Key Concepts & Vocabulary
TermDefinitionExample
UnitA standard, defined quantity used as a basis for measurement.The 'second' is the base unit of time in the International System of Units (SI). 'Minute' and 'hour' are also common units of time.
Conversion FactorA ratio or fraction which represents the relationship between two different units and is equal to one. It's the tool we use to change units.Since 60 seconds = 1 minute, the conversion factors are (60 seconds / 1 minute) and (1 minute / 60 seconds). Both fractions equal 1.
Dimensional AnalysisA problem-solving method that uses the fact that any number can be multiplied by one without changing its value. It involves strategically multiplying by conversion factors to cancel out unwanted units and leave the desired units.To co...
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Core Formulas
The Conversion Factor Principle
\text{Given Quantity} \times \frac{\text{Desired Unit}}{\text{Given Unit}} = \text{Result in Desired Unit}
To convert a quantity, multiply it by a conversion factor. Arrange the fraction so that the unit you want to get rid of (the 'Given Unit') is in the denominator, allowing it to cancel out, and the unit you want to end up with (the 'Desired Unit') is in the numerator.
Multi-Step Conversion (Chain Conversion)
\text{Qty} \times \frac{\text{Unit B}}{\text{Unit A}} \times \frac{\text{Unit C}}{\text{Unit B}} = \text{Result in Unit C}
For conversions that require multiple steps (e.g., days to seconds), you can chain conversion factors together. Ensure the numerator of one factor cancels the denominator of the next term in the...
4 more steps in this tutorial
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Challenging
A red light flashes every 90 seconds. A blue light flashes every 4 minutes. If they flash together at 3:00 PM, at what time will they next flash together?
A.3:06 PM
B.3:08 PM
C.3:10 PM
D.3:12 PM
Challenging
A computational task is projected to take `(t^2 - 4)` minutes to run, where `t` is a parameter related to data size. Which rational expression represents the time in days?
A.(t^2 - 4) / 1440
B.60(t^2 - 4)
C.(t^2 - 4) / 24
D.(t^2 - 4) / 86400
Challenging
A student attempts to convert a speed of 72 km/h to m/s. Their calculation is: `(72 km / 1 h) × (1000 m / 1 km) × (60 min / 1 h)`. They get an answer of 4,320,000 m/h. What is their fundamental error in applying dimensional analysis?
A.They used 100 m in a km instead of 1000 m.
B.They did not set up the factors to cancel the 'hours' unit correctly.
C.They should have converted to seconds directly, not minutes.
D.Their final arithmetic calculation is wrong.
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