Compute the Laplace transform of sin t (assume unilateral transform and zero initial conditions).

Difficulty: Easy

Correct Answer: 1 / (s^2 + 1)

Explanation:


Introduction / Context:
The Laplace transform converts time-domain signals to the s-domain, simplifying differential equations to algebraic forms. Trigonometric inputs such as sin t and cos t are classics, and remembering their transforms is essential for solving control and circuit problems quickly.



Given Data / Assumptions:

  • Function: f(t) = sin t for t ≥ 0.
  • Unilateral Laplace transform definition is used.
  • Zero initial conditions; standard transform tables apply.


Concept / Approach:
The standard Laplace transform of sin(ω t) is ω / (s^2 + ω^2). Setting ω = 1 yields 1 / (s^2 + 1). This can also be derived via integration using Euler’s identities or by differentiating the transform of cos t with respect to s.



Step-by-Step Solution:

Use identity: L{sin(ω t)} = ω / (s^2 + ω^2).Set ω = 1 ⇒ L{sin t} = 1 / (s^2 + 1).Confirm dimensions: numerator is frequency (1), denominator is quadratic in s.


Verification / Alternative check:
Differentiate the transform pair L{cos t} = s / (s^2 + 1) with respect to s and apply relationships between sin and cos to reconfirm the result.



Why Other Options Are Wrong:

s / (s^2 + 1) — this is the transform of cos t, not sin t.1 / (s + 1) and s / (s + 1) — correspond to exponential or step-related transforms, not sinusoidal functions.


Common Pitfalls:
Swapping the transforms of sin t and cos t; remember sin has numerator ω, cos has numerator s.



Final Answer:
1 / (s^2 + 1)

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