Transforming Cosine with Unit Step?

In summary, the Laplace transform of cos(t)h(t) is 1/s. The unit step function does not affect the transform and can be treated as 1. Similarly, the Laplace transform of (e^-3t + 2)h(t) is 1/(s+3) + 2/s. The presence of the step function in this case would effectively give the one-sided transform.
  • #1
meb09JW
23
0

Homework Statement



Find the Laplace transform of cos(t)h(t)
if the LT of h(t) (unit step) is 1/s


Homework Equations



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The Attempt at a Solution



Since the unit step isn't shifting anything anywhere, can I just treat it as 1? Seems too simple, haha. Any ideas? thanks.
 
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  • #2
Here's a similar one - Find the LT of (e^-3t + 2)h(t)
with h(t) the same as before.

Would the h(t) just act as a 'turn on' in these cases?
 
  • #3
Yes, and as you noted, it's superfluous with the usual Laplace transform. If you are using the double-sided transform, the presence of the step function would effectively give you the one-sided transform.
 
  • #4
Ok, thanks.

meb09JW said:
Here's a similar one - Find the LT of (e^-3t + 2)h(t)
with h(t) the same as before.

So would the above LT simply be-

1/(s+3) + 2/s

?
 
  • #5
Yup.
 

1. What is the definition of a unit step function in Laplace transform?

The unit step function, denoted as u(t), is a mathematical function that takes on the value of 0 for all negative values of t and the value of 1 for all positive values of t. In Laplace transform, it is represented by the Heaviside function H(t), and is used to represent a sudden change or "step" in a system.

2. How is the unit step function used in solving differential equations?

The unit step function is used in solving differential equations by transforming the original equation into an algebraic equation using Laplace transform. This allows for easier manipulation and solution of the equation, as well as the ability to solve for the output of a system for different inputs.

3. Can the unit step function be used for non-linear systems?

Yes, the unit step function can be used for non-linear systems. However, in these cases, the Laplace transform technique may not provide an exact solution and may require additional methods such as numerical methods or approximations.

4. How does the unit step function relate to the Dirac delta function?

The unit step function can be thought of as the integral of the Dirac delta function. In other words, the unit step function is the accumulated effect of the Dirac delta function over time. This relationship is especially useful in solving differential equations with impulse inputs.

5. Are there any real-world applications of the unit step function in Laplace transform?

Yes, the unit step function in Laplace transform has many real-world applications, particularly in control systems and signal processing. It is used to model and analyze systems with sudden changes, such as in electrical circuits, mechanical systems, and communication systems.

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