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Match List I with List II.

List IList II
(a) Laplace transform of sinωt(i) \(\frac{s}{s^{2}+\omega^{2}}\)
(b) Laplace transform of cosωt(ii) \(\frac{\omega}{s^{2}+\omega^{2}}\)
(c) Laplace transform of sinhωt(iii) \(\frac{s}{s^{2}-\omega^{2}}\)
(d) Laplace transform of coshωt(iv) \(\frac{\omega}{s^{2}-\omega^{2}}\)

Choose the most appropriate answer from the options given below :

  • A.(a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
  • B.(a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
  • C.(a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
  • D.(a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)

Answer: D

The correct matching is (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii).

The standard Laplace transforms are:

  • \(\sin\omega t \rightarrow \frac{\omega}{s^{2}+\omega^{2}}\), item (ii)
  • \(\cos\omega t \rightarrow \frac{s}{s^{2}+\omega^{2}}\), item (i)
  • \(\sinh\omega t \rightarrow \frac{\omega}{s^{2}-\omega^{2}}\), item (iv)
  • \(\cosh\omega t \rightarrow \frac{s}{s^{2}-\omega^{2}}\), item (iii)

A quick check: the sine-type functions start at zero, so their transforms carry \(\omega\) in the numerator, while cosine-type functions start at one and carry \(s\). The hyperbolic pair has a minus sign in the denominator. Option (a)-(i), (b)-(ii) is the common trap of pairing sine with \(s\).

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