Value of g used on Earth?

9.8 m s^{-2} unless told otherwise.

Does mass change on the Moon?

No. Mass is the same everywhere; only weight changes.

Newton's second law with SI units?

F=ma, with F in N, m in kg, a in m s^{-2}.

How can units check a formula?

Replace each quantity by its unit, simplify, and see whether both sides have the same unit.

Quantities and units in mechanicsAQA A-Level Maths: Flashcards

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Three fundamental quantities in mechanics and their SI units?

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Three fundamental quantities in mechanics and their SI units?: Length (m), time (s), mass (kg).
SI unit of velocity?: m s $^{-1}$ .
SI unit of acceleration?: m s $^{-2}$ .
What is a newton in base SI units?: $1$ N $=1$ kg m s $^{-2}$ .
Is weight a mass or a force?: A force, measured in newtons.
Formula for weight?: $W=mg$ .
Value of $g$ used on Earth?: $9.8$ m s $^{-2}$ unless told otherwise.
Does mass change on the Moon?: No. Mass is the same everywhere; only weight changes.
Newton's second law with SI units?: $F=ma$ , with $F$ in N, $m$ in kg, $a$ in m s $^{-2}$ .
Convert $36$ km h $^{-1}$ to m s $^{-1}$ .: $36\div3.6=10$ m s $^{-1}$ .
Convert $5$ m s $^{-1}$ to km h $^{-1}$ .: $5\times3.6=18$ km h $^{-1}$ .
Weight of a $15$ kg crate on Earth?: $15\times9.8=147$ N.
How can units check a formula?: Replace each quantity by its unit, simplify, and see whether both sides have the same unit.

Exam questions on Quantities and units in mechanics

A crate of mass $15$ kg rests on a table. Take $g=9.8$ m s $^{-2}$ on Earth.
The crate is taken to the Moon, where $g=1.6$ m s $^{-2}$ . State its mass and find its weight there.2 marks
A cyclist travels $1.2$ km in $4$ minutes at a constant speed along a straight road.
The cyclist then speeds up uniformly from $5$ m s $^{-1}$ to $8$ m s $^{-1}$ in $6$ s. Find the acceleration, including its unit.2 marks
A trolley of mass $8$ kg is pulled across a smooth horizontal floor by a resultant horizontal force of $20$ N. Take $g=9.8$ m s $^{-2}$ .
Find the acceleration of the trolley, and show that the unit you use for acceleration is consistent with $1$ N being $1$ kg m s $^{-2}$ .3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).