Year 9 Science · Unit 4 · Lesson 14
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Learning Goals
Acceleration formula practice
Use the formula a = (v − u) ÷ t to calculate acceleration for each scenario. Show your working. Use a negative answer for deceleration.
Where: a = acceleration (m/s²), v = final speed (m/s), u = initial speed (m/s), t = time (s)
| # | Scenario | Working (a = (v−u) ÷ t) | Answer |
|---|---|---|---|
| 1 | Car accelerates from 0 to 25 m/s in 5 s | ||
| 2 | Cyclist goes from 10 m/s to 25 m/s in 15 s | ||
| 3 | Braking car slows from 30 m/s to 0 in 6 s | ||
| 4 | Aircraft accelerates from 0 to 80 m/s in 40 s |
Real-world scenario — skydiving
A skydiver jumps from a plane. Phase 1 (0–15 s): speed increases from 0 to 53 m/s. Phase 2 (15–30 s): speed slowly increases then levels out at 57 m/s — terminal velocity is reached. Phase 3: the parachute opens and speed drops from 57 m/s to 6 m/s in just 5 seconds.
(a) Calculate the acceleration during Phase 1. Show your working using a = (v − u) ÷ t.
(b) Explain why the skydiver reaches terminal velocity at the end of Phase 2. Use the words gravity, air resistance, and balanced forces in your answer.
(c) Calculate the deceleration (negative acceleration) during Phase 3 when the parachute opens. Show your working.
Wrap Up
In one sentence, what was the main idea of this lesson?