WAEC 2020 Physics · Question 25
A motorcycle starting from rest is uniformly accelerated such that its velocity in 10s is 72kmhr. What is its acceleration?
Options
- A.108ms
- B.86ms
- C.4ms
- D.2ms
Answer: D. 2ms
Explanation written with AI and checked against the answer key
Analyze the question: The motorcycle starts from rest (u = 0), reaches a velocity v = 72 km/h in t = 10 s. We need the acceleration a. Concept: For uniform acceleration, a = (v − u) / t Units must be consistent, so convert km/h to m/s first. Conversion: 72 km/h = 72 × 1000 m / 3600 s = 72 × (5/18) = 20 m/s Solution: a = (20 − 0) / 10 = 2 m/s² Check the options: The options are written as "ms²", but they clearly mean m/s² (ms⁻²). Answer: D (2 m/s²) Tip: To convert km/h to m/s, multiply by 5/18. Many students lose marks by plugging 72 straight into the formula. If you did that, you would get 7.2, which is not an option, a sign that something is wrong. Also, 72 is a handy number because 72 × 5/18 = 20 exactly. Always convert units before substituting.AI can make mistakes. Report anything that looks wrong.
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