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AQA A Level Maths: Mechanics復習筆記1.1.3 Derived Units

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年7月14日上午11:15

Derived units for quantities such as velocity, acceleration and force etc. are combinations of S.I. units
- Speed?or?Velocity?= distance ÷ time?=?m/s or m s-1?(Velocity is just speed with direction)
- Acceleration?= velocity ÷ time?=?ms-1?/s =?m/s2?or m s-2
- Weight?or?Force?=?mass?x acceleration =?kg m s-2?or N?(N = Newtons)

1-1-3-diagram-1

1.1.3_WE_Derived-Units_1-1

a) Convert the following into S.I. units

i) 72 km h-2? ? ? ? ? ? ? ? ? ? ii)? ?50 cm per minute? ? ? ? ? ? ? ? ? ?iii)? ?14 g cm-3

1-1-3-worked-solution-a

b) A cyclist takes 15 minutes to travel 2.54 km. Calculate the average speed in m s-1?

1-1-3-worked-solution-b

Watch out for exam questions using non S.I. units such as feet and inches or miles per hour.
Make sure you are confident?converting?between these derived units,
Remember?speed?is velocity without direction and?weight?is a force measured in?Newtons, not a mass measured in kg.
If you ever forget a formula, use the units it is measured in to figure it out,
e.g. m/s = metres?÷?seconds = distance?÷?time = velocity.

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