Example: Planes fly at typical speeds of around 250 m/s. Calculate the distance travelled by a plane moving at this speed for 2 hours.
Step 1: List the known quantities
Speed, v = 250 m/s
Time, t = 2 hoursStep 2: Write the relevant equation
v = s/tStep 3: Rearrange for distance travelled, s
s = v × tStep 4: Convert any units
The time given in the question is not in standard units
Convert 2 hours into seconds:
2 hours = 2 × 60 ×60 = 7200 sStep 5: Substitute in the values for speed and time
s = 250 × 7200 = 1 800 000 m
Example: Florence Griffith Joyner set the women’s 100 m world record in 1988, with a time of 10.49 s. Calculate her average speed during the race.
Step 1: List the known quantities
Distance, s = 100 m
Time, t = 10.49 sStep 2: Write the relevant equation
Sprinters typically speed up out of the blocks up to some maximum speed
Because Florence’s speed changes over the race, we can calculate her average speed using the equation:
average speed = total distance ÷ time takenStep 3: Check any unit conversions
Check that all quantities given in the question are in standard units
In this example, they are all in standard unitsStep 4: Substitute the values for total distance and time
Average speed = 100 ÷ 10.49 = 9.53288... = 9.53 m/s
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