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:
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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