A signal f(t) has the Laplace transform F(s) = (s + 15)/(s² + 9s + 13). Find the initial slope f′(0⁺) with the initial value theorem.
Laplace transforms worksheet with answers
1.Easy
F(s) = (s + 15)/(s² + 9s + 13)
f′(0⁺) =
2.Easy
A signal f(t) has the Laplace transform F(s) = 9(s + 2)/(s(s + 3)(s + 6)). Use the final value theorem to find the value f(∞) that f(t) settles to.
F(s) = 9(s + 2)/(s(s + 3)(s + 6))
f(∞) =
3.Medium
Find f(t) for F(s) = (3s + 22)/(s² + 4s + 8) by completing the square, and evaluate f(0.2).
F(s) = (3s + 22)/(s² + 4s + 8)t = 0.2 s
f(0.2) =
4.Medium
Find f(t) for F(s) = (s + 21)/(s² + 10s + 25) and evaluate f(0.25).
F(s) = (s + 21)/(s² + 10s + 25)t = 0.25 s
f(0.25) =
5.Hard
A system obeys y″ + 7y′ + 10y = 50·u(t). It starts at rest (y(0) = 0, y′(0) = 0) and the input is a step u(t) = 2 for t ≥ 0. Use the Laplace transform to find the output y(0.2).
y″ + 7y′ + 10y = 50·u(t)u(t) = 2y(0) = 0, y′(0) = 0t = 0.2 s
y(0.2) =
6.Hard
Solve y″ + 4y′ + 3y = 0 with y(0) = 1 and y′(0) = −9 using the Laplace transform, and find y(0.4).
y″ + 4y′ + 3y = 0y(0) = 1y′(0) = −9t = 0.4 s
y(0.4) =
Answer key
- 1. f′(0⁺) = 6
- 2. f(∞) = 1
- 3. f(0.2) = 3.94
- 4. f(0.25) = 1.433
- 5. y(0.2) = 1.281
- 6. y(0.4) = −0.8062
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