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AQA A Level Maths: Mechanics复习笔记1.1.3 Derived Units

Category: A-level课程, 教材笔记, 福利干货 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.

转载自savemyexams

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