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AS Daily A Level Physics question

2026-02-06 OCR A Mechanics — Kinematics (suvat) OCR-A Module 3.1 Kinematics: motion in a straight line OCR-A Module 3.1.2 Equations of motion for uniform acceleration (suvat)

An athlete accelerates uniformly from rest along a straight track for 20 m, reaching speed v at the end of this phase. On a second attempt, the athlete doubles the acceleration but sustains it for only 10 m. Ignoring air resistance, what is the new speed at the end of the acceleration phase compared with v?

  1. A It decreases to 0.71 v
  2. B No change: it is still v (correct)
  3. C It increases to 1.41 v
  4. D It doubles to 2.0 v

Answer

The correct answer is B.

Correct: B — No change: it is still v. A ignores the doubled acceleration and treats speed as depending only on distance, giving v_new/v_old = sqrt(1/2) ≈ 0.71. B uses v^2 ∝ a s from uniform acceleration with u = 0, so v_new/v_old = sqrt((2a × 10)/(a × 20)) = sqrt(1) = 1. C considers only the doubled acceleration and ignores the halved distance, giving an incorrect factor sqrt(2). D assumes speed is proportional to acceleration (or uses v = at) without accounting for the shorter distance and different time, leading to an overestimate.

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