Laplace Transform of Mass-Spring-Damper System

Published on May 29, 2025

Calculus

Find the Laplace Transform of the solution for a mass-spring-damper system with an applied force, given initial conditions. The solution involves setting up the differential equation, applying the Laplace Transform, and solving for X(s).

Question

Answer

Hereโ€™s a step-by-step solution to the problem:
The problem describes a mass-spring-damper system with an external force. We need to set up the differential equation for the system and then find the Laplace Transform of its solution.
1. Identify the given parameters and forces:
  • Mass,
  • Spring constant,
  • Damping force: The damping constant is โ€œtwice the velocityโ€. This means the damping force is proportional to the velocity, . The problem states โ€œdamping constant of twice the velocityโ€, which is a bit ambiguous. However, in the context of a damping force , if the damping constant itself is โ€œtwice the velocityโ€, it would imply , making the damping force , which is non-linear. A more standard interpretation for โ€œdamping constant of twice the velocityโ€ in a linear system is that the damping coefficient is 2. Letโ€™s assume the damping force is .
  • Applied force, (positive force)
2. Formulate the differential equation:
The general form of the equation of motion for a mass-spring-damper system is:
Where:
  • is the inertial force.
  • is the damping force.
  • is the spring force (restoring force).
  • is the external applied force.
Substitute the given values into the equation:
So, the differential equation is:
3. Apply the Laplace Transform:
We need to find the Laplace Transform of the solution, .
The initial conditions are given as and .
Recall the Laplace Transform properties:
  • (for a constant C)
Apply the Laplace Transform to each term in the differential equation:
Using the initial conditions and :
Substitute these back into the transformed equation:
4. Solve for :
Factor out from the left side:
Now, isolate :
This is the Laplace Transform of the solution .
The final answer is .