When can you use the SUVAT equations?

Only when acceleration is constant (uniform). For changing acceleration — air resistance, terminal velocity questions — use velocity-time graphs and areas instead.

How do you approach projectile questions?

Split the motion into two independent columns: horizontal (constant velocity) and vertical (constant acceleration g). Time is the only quantity shared between them — usually found from the vertical column first.

How is g measured in the lab?

Standard method: time a steel ball falling through a measured height using an electronic timer with release and trapdoor switches, then use s = ½gt². Plot s against t² and take g as twice the gradient.

← Edexcel IAL Physics revision

Edexcel IAL Physics revision · AS — Mechanics

Kinematics

IGCSE motion returns with equations instead of graph-reading — and with projectiles, the first genuinely two-dimensional problem most students meet. The whole topic is won by one discipline: choose a positive direction and never betray it.

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What the syllabus demands

—Define displacement, velocity and acceleration as vectors
—Use the four uniform-acceleration (SUVAT) equations
—Interpret and sketch displacement-time and velocity-time graphs
—Describe free fall; determine g experimentally
—Analyse projectile motion: independent horizontal and vertical components

Definitions that earn marks

Clear definitions to practise — check your course mark scheme

Displacement: The distance travelled in a stated direction — the vector version of distance.
Velocity: The rate of change of displacement.
Acceleration: The rate of change of velocity.

The equations

SUVAT 1v = u + at

SUVAT 2s = ut + ½at²

SUVAT 3v² = u² + 2as

SUVAT 4s = ½(u + v)t

More equations to practise: the Edexcel IAL formula sheet.

Where the marks die

Common mistakes to check

01
Using SUVAT when acceleration is not constant. The equations are valid only for uniform acceleration — if the question mentions air resistance building up, SUVAT is dead and graphs take over.
02
Sign chaos in vertical motion. Choose up as positive: then g = −9.81 m/s², a downward velocity is negative, and the algebra takes care of itself. Most projectile errors are sign errors.
03
Mixing the components of projectile motion. Horizontal: constant velocity, no acceleration. Vertical: constant acceleration g. They share only the time — solve them in separate columns.
04
Reading 'deceleration of 3 m/s²' and substituting +3. If your positive direction is the direction of motion, deceleration is negative.

One worked example, done properly

Question

A ball is thrown horizontally at 15 m/s from a cliff 45 m high. How far from the base does it land? (g = 9.81 m/s²)

Method

1.Vertical (down positive): 45 = ½ × 9.81 × t², so t² = 9.17, t = 3.03 s.
2.Horizontal: constant velocity, s = vt = 15 × 3.03.

s ≈ 45 m from the base

Test yourself

10 questions · instant marking

Question 1 of 10

The SUVAT equations are valid only when:

Question 2 of 10

A ball is thrown vertically upwards. At its highest point:

Question 3 of 10

A car accelerates uniformly from 5 m/s to 25 m/s over 100 m. Using v² = u² + 2as, the acceleration is:

Question 4 of 10

In projectile motion (no air resistance), the horizontal velocity:

Question 5 of 10

The gradient of a displacement-time graph gives:

Question 6 of 10

A stone is dropped from rest. How far does it fall in 3.0 s? (g = 9.81 m/s²)

Question 7 of 10

A projectile is launched at 20 m/s at 30° above horizontal. Its initial vertical velocity is:

Question 8 of 10

An object decelerates uniformly from 30 m/s to rest in 6 s. The distance travelled is:

Question 9 of 10

Two balls are released from the same height: one dropped, one thrown horizontally. Ignoring air resistance, they land:

Question 10 of 10

A velocity-time graph shows a straight line crossing from positive to negative velocity. This means the object:

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