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AS Daily A Level Physics question

2025-12-18 OCR A Mechanics & Materials (M3) 3.4.1(b) 3.4.1(c)

In a lab test, two identical light springs are used to support the same hanging weight W. Setup S has the springs connected one below the other; Setup P has the springs side by side attached to the same top support and the same hook carrying W. The springs behave elastically in the range used. Without calculating any constants, which statement about the total extension compared with a single spring supporting W must be true?

  1. A Both setups give the same extension as a single spring supporting the weight W.
  2. B Series gives half the extension of a single spring; parallel gives twice the extension.
  3. C Series gives twice the extension of a single spring; parallel gives half the extension. (correct)
  4. D Series gives four times the extension; parallel gives one-quarter of the extension.

Answer

The correct answer is C.

Correct: C — Series gives twice the extension of a single spring; parallel gives half the extension. A This ignores that in series each spring carries the full weight so the extensions add, while in parallel identical springs share the load so the extension is reduced. B In series the extension is not halved; it doubles because both springs experience the same force and their extensions add, and in parallel the force splits so the extension is not larger. C This is the only statement consistent with load sharing in parallel and extension adding in series for identical linear springs. D Factors of four and one-quarter imply a squared effect; for linear springs the effective stiffness merely doubles in parallel and halves in series, giving factors of two, not four.

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