Constant acceleration practice problems Edexcel IAL Mechanics 1, Chapter 2
Displacement-time and velocity-time graphs, the five constant acceleration (suvat) formulae, and vertical motion under gravity. Try each question before you look: use the hint if you are stuck, then reveal the worked solution one step at a time.
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Key equations for constant acceleration
| v = u + at | no s |
|---|---|
| s = ½(u + v)t | no a |
| v2 = u2 + 2as | no t |
| s = ut + ½at2 | no v |
| s = vt − ½at2 | no u |
| area under a v-t graph | displacement; the gradient is acceleration |
Take g = 9.8 m s−2, as the WME01 paper asks, and give answers to 2 or 3 significant figures. Answers within 2.5% are marked correct, so rounding along the way is fine. Revise the methods in our A level Maths mechanics guide.
Warm-up questions
Quick checks on the core ideas. If these feel easy, go straight to the exam-style questions.
Hint
You know u, v and t. Which suvat formula links them with a?
Worked solution
- Use v = u + at: 16 = 4 + 6a.
- 6a = 12, so a = 2 m s−2.
Hint
u = 0, a = 3, t = 5. You want s.
Worked solution
- Use s = ut + ½at2 with u = 0.
- s = ½ × 3 × 52 = 37.5 m.
Hint
Area is velocity multiplied by time.
Worked solution
- Velocity × time gives displacement.
- So the area is the displacement: B. The gradient is the acceleration.
Exam-style questions
Questions at the level of the Edexcel IAL Mechanics 1 exam. The ones marked Challenge combine more than one idea.
Hint
At the greatest height v = 0. Take upwards as positive, so a = −9.8.
Worked solution
- Upwards positive: u = 14.7, v = 0, a = −9.8.
- v2 = u2 + 2as: 0 = 14.72 − 2 × 9.8 × s.
- s = 216.09/19.6 = 11.0 m (3 s.f.).
Hint
When it returns, the displacement s = 0.
Worked solution
- s = ut + ½at2: 0 = 14.7t − 4.9t2 = t(14.7 − 4.9t).
- t = 0 is the start, so t = 14.7/4.9 = 3 s.
Hint
You know u, v and s. Leave out t.
Worked solution
- v2 = u2 + 2as: 82 = 202 + 2 × a × 84.
- 64 = 400 + 168a, so a = −2.
- The deceleration is 2 m s−2.
Hint
Take downwards as positive, so a = +9.8 and s = +50.
Worked solution
- Downwards positive: u = 4, a = 9.8, s = 50.
- v2 = 42 + 2 × 9.8 × 50 = 996.
- v = 31.6 m s−1 (3 s.f.).
Hint
When P catches Q they have both travelled the same distance from the lights.
Worked solution
- Distance for P: s = ½ × 2 × t2 = t2. Distance for Q: s = 12t.
- t2 = 12t, so t(t − 12) = 0.
- t = 0 is the start, so P catches Q after 12 s, 144 m from the lights.
Exam question practice
One original structured question in the style of the WME01 paper. Answer it in full, with working, before you open the mark scheme: M marks are for a correct method, A marks for accurate answers that follow from it, and B marks for a correct statement on its own.
Structured exam question style · 7 points · about 10 minutes
A train starts from rest at station A. It accelerates uniformly for 20 s to a speed of V m s−1, travels at this speed for 60 s, then decelerates uniformly for 10 s, coming to rest at station B. The distance from A to B is 1.8 km.
- (a) Sketch a speed-time graph for the journey.
- (b) Find the value of V.
- (c) Find the deceleration of the train.
Write your full answer on paper first, then open the scoring guide and tick each point you earned.
Scoring guide and model answer
Part (a)
A trapezium: a straight line from (0, 0) up to (20, V), horizontal to (80, V), then straight down to (90, 0).
Part (b)
Area = ½(90 + 60)V = 75V = 1800, so V = 24.
Part (c)
Deceleration = 24/10 = 2.4 m s−2.
Your mark: 0 of 7
Common mistakes in constant acceleration
- Mixing up directions: choose a positive direction at the start, and give g a minus sign if up is positive.
- Using suvat when the acceleration is not constant (for example across two stages of a journey). Split the motion into stages.
- Forgetting that 1.8 km is 1800 m.
- Giving too many significant figures after using g = 9.8. Give 2 or 3.
Keep going
Revise the ideas behind these questions:
Then try real exam questions: Edexcel IAL Mechanics 1 past papers, with official scoring guidelines. · All Edexcel IAL Mechanics 1 units