CSEC ADDITIONAL MATHEMATICS · SECTION 3 · LESSON C4

Rates of Change: Kinematics and Related Rates

The derivative as a rate of change, velocity and acceleration as derivatives of displacement, velocity–time graphs, and related rates of change for areas and volumes.

Introductory CalculusS3 A.11S3 A.12≈ 45 min🎮 3 games
Before you start

By the end of this lesson you can…

Step 1 · Watch

Explainer video

5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.

LESSON C4 · EXPLAINER

Rates of Change: Kinematics and Related Rates

Velocity is the rate of change of displacement. Acceleration is the rate of change of velocity. Differentiate once, then again — and you describe all motion.

Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.

Explore in 3D

Kinematics

Move through time and watch displacement, velocity and acceleration.

Step 2 · Read

Key notes

Copy these into your notebook in your own words — that is how they stick.

Velocity

v = ds/dt.

Acceleration

a = dv/dt = d²s/dt².

At rest

v = 0.

Total distance

Split at the times when v = 0 and add the absolute displacements.

Gradient of v–t graph

Acceleration; area gives distance.

Related rates

dy/dt = dy/dx × dx/dt.

Common formulae

Sphere V = (4/3)πr³, S = 4πr²; circle A = πr²; cube V = x³.

Units

m/s, m/s², cm³/s — state them.

EXAM TIPS & COMMON MISTAKES

  • Total distance ≠ final displacement: split the journey where the velocity changes sign.
  • Write the formula, differentiate, then substitute — do not substitute early.
  • Check units: rate of volume change in cm³/s, rate of area change in cm²/s.
  • a = 0 gives the maximum or minimum VELOCITY (a stationary point of v).
Play & practise

Games

3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Additional Mathematics Arcade.

Step 3 · Practise

Paper 1 practice — multiple choice

8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.

CSEC Paper 01 style · SO A.11

1. A particle moves with displacement s = t³ − 6t² + 9t. Its velocity at time t is

Answer: B. ds/dt.
CSEC Paper 01 style · SO A.11

2. For s = t³ − 6t² + 9t, the particle is at rest when t equals

Answer: C. 3(t − 1)(t − 3) = 0.
CSEC Paper 01 style · SO A.11

3. For s = t³ − 6t² + 9t, the acceleration at t = 1 is

Answer: D. a = 6t − 12.
CSEC Paper 01 style · SO A.11

4. The total distance travelled in the first 3 s for s = t³ − 6t² + 9t is

Answer: A. 4 forward and 4 back.
Adapted from CSEC P1 May/June 2024 (velocity–time graph item)

5. The gradient of a velocity–time graph represents

Answer: B. dv/dt.
CSEC Paper 01 style · SO A.11

6. The radius of a sphere increases at 0.5 cm/s. When r = 4 cm, dV/dt is

Answer: C. 4π(16)(0.5).
CSEC Paper 01 style · SO A.11

7. The edge x of a cube increases so that dV/dt = 12 when x = 2. Then dx/dt equals

Answer: B. 12 = 3(4)dx/dt.
CSEC Paper 01 style · SO A.11

8. If s = 2t³ − 9t² + 12t, the acceleration is

Answer: D. 6t² − 18t + 12 → 12t − 18.
Step 4 · Apply

Paper 2 practice — structured questions

Write full answers, then reveal the mark scheme and tick the points you earned (26 marks in total). Show all your working — method marks count. Your answers are saved on this device.

CSEC Paper 02 style · Section 3 (Kinematics)

Question 1 [14 marks]

A particle moves in a straight line so that its displacement s metres from a fixed point O at time t seconds is s = 2t³ − 9t² + 12t.

(a) Find expressions for the velocity and acceleration of the particle. [2]

MARK SCHEME — (a) (max 2)

(b) Find the values of t at which the particle is at rest. [3]

MARK SCHEME — (b) (max 3)

(c) Find the displacement of the particle at each of these times. [2]

MARK SCHEME — (c) (max 2)

(d) Find the acceleration at each of these times and state what it shows. [3]

MARK SCHEME — (d) (max 3)

(e) Find the total distance travelled in the first 3 seconds. [4]

MARK SCHEME — (e) (max 4)

CSEC Paper 02 style · Section 3 (Related rates)

Question 2 [12 marks]

A spherical balloon is inflated so that its radius increases at a constant rate of 0.5 cm/s.

(a) Find the rate of increase of the volume when the radius is 4 cm, leaving your answer in terms of π. [4]

MARK SCHEME — (a) (max 4)

(b) Find the rate of increase of the surface area S = 4πr² at that instant. [3]

MARK SCHEME — (b) (max 3)

(c) The edge x of a cube is increasing so that the volume increases at 12 cm³/s. Find dx/dt when x = 2. [3]

MARK SCHEME — (c) (max 3)

(d) Explain why dV/dt = dV/dr × dr/dt. [2]

MARK SCHEME — (d) (max 2)

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Sources

Where this topic appears in CSEC papers

Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.