Is this formula given in the exam?

No. SPM Physics papers provide no formula sheet, so this must be recalled.

When can I use v = u + at?

Only when the acceleration is uniform (constant) and the motion is along a straight line. If the acceleration changes during the motion, this equation does not apply.

How do I handle an object that is slowing down?

Slowing down is a deceleration, so substitute a negative value for a . For example, if the object decelerates at 2 m s⁻² you use a = −2 m s⁻². Keep the direction signs consistent with the initial velocity.

What are the SI units for each symbol?

v and u are in m s⁻¹, a is in m s⁻², and t is in s. If time is given in minutes, convert it to seconds before substituting.

First equation of motion Formula, SPM Physics

First equation of motion

v = u + at

Not given in the exam, recall it.

What it is for

First equation of motion is used in Force and Motion I (SPM Physics Form 4). Keep the SI units in every line of working. Force and Motion I

Symbols and SI units

Symbol	Meaning	SI unit
`v`	final velocity	m s⁻¹
`u`	initial velocity	m s⁻¹
`a`	acceleration	m s⁻²
`t`	time	s

Rearrangements

a = (v − u) / t
t = (v − u) / a
u = v − at

Worked example

A car speeds up from u = 10 m s⁻¹ at a = 2 m s⁻² for t = 5 s. v = u + at = 10 + (2 × 5) = 20 m s⁻¹.

Common trap

Valid only for uniform (constant) acceleration. Treat deceleration as a negative a and keep direction signs consistent.

Understanding the first equation of motion

The equation v = u + at links four quantities for motion in a straight line under uniform acceleration. Here v is the final velocity in m s⁻¹, u is the initial velocity in m s⁻¹, a is the acceleration in m s⁻², and t is the time in s.

The relationship simply says that velocity changes at a steady rate: every second, the velocity gains a more metres per second, so after t seconds the velocity has risen by at above the starting value u.

To find acceleration: a = (v − u) / t
To find time: t = (v − u) / a
To find the initial velocity: u = v − at

Rearranging first, then substituting, keeps the working tidy and reduces slips.

A worked example, step by step

A train pulls away from a station with an initial velocity u = 6 m s⁻¹ and accelerates uniformly at a = 1.5 m s⁻² for t = 8 s. Find its final velocity.

Write the formula, then substitute the values with their units:

v = u + at
v = 6 m s⁻¹ + (1.5 m s⁻² × 8 s)
v = 6 m s⁻¹ + 12 m s⁻¹

So v = 18 m s⁻¹.

The unit of at works out as m s⁻² × s = m s⁻¹, which matches the unit of velocity, confirming the equation is dimensionally consistent. The answer is quoted to two significant figures, matching the data given.

Common mistakes and how this is tested

The main trap is that this equation is valid only for uniform (constant) acceleration; it cannot be used when the acceleration changes. Other frequent errors:

Treating a deceleration as positive. Slowing down means a is negative, for example a = −2 m s⁻².
Swapping u and v, which reverses the sign of the change.
Leaving time in minutes instead of converting to seconds.

In the paper this appears under command words such as calculate and determine the final velocity, and under define when asked to state acceleration. Always show the formula, the substitution, and the unit on the final line.

Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)

Written by the spmphysics.com.my editorial team.· Updated 5 Sept 2026