Physics

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Conservation of Momentum Calculator.

Calculate the common velocity after a one-dimensional perfectly inelastic collision.

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01

Set your values

Results update as you type.

totalMomentum: 5 kg·m/s

totalMomentum

0.000000kg·m/s
finalVelocity: 1 m/s

finalVelocity

0.000000m/s
totalMass: 5 kg

totalMass

0.000000kg

Results update automatically as you type.

This page applies only the stated idealized equation and explicit inputs; verify specialized engineering, medical, or safety decisions against applicable standards.

Use Cases

Physics homework and exam prep

Quickly verify your manual calculations for perfectly inelastic collision problems, ensuring you understand the concept of momentum conservation.

Example: Check the final velocity when a 2 kg object moving at 3 m/s hits a 1 kg object at rest.

Engineering design and safety analysis

Estimate the post-impact velocity of coupled masses in systems like train couplings or crash simulations, aiding in preliminary design decisions.

Example: Determine the common velocity of two railcars after coupling.

Frequently Asked Questions

What is a perfectly inelastic collision?
A perfectly inelastic collision is one where two objects collide and stick together, moving with a common velocity after impact. Kinetic energy is not conserved, but momentum is conserved.
How is the common velocity calculated?
The common velocity is found using conservation of momentum: (m1*v1 + m2*v2) / (m1 + m2). This calculator uses the masses and velocities you input to compute that value.
Can velocities be negative?
Yes, velocities can be negative to indicate direction. The calculator uses the sign of the velocity in the momentum calculation, so a negative velocity will affect the resulting common velocity.

Tips & Common Mistakes

Tips

  • Ensure masses are in kilograms and velocities in meters per second for consistent results.
  • Use the sign of velocity to indicate direction; positive for one direction, negative for the opposite.
  • Remember that this calculator assumes a perfectly inelastic collision (objects stick together).
  • Double-check your inputs for accuracy, as small errors in mass or velocity can significantly affect the result.

Common Mistakes to Avoid

  • Forgetting to include the sign of velocity, which can lead to incorrect momentum sums.
  • Using inconsistent units, such as grams instead of kilograms, without converting.
  • Assuming kinetic energy is conserved, which is not true for perfectly inelastic collisions.

Last updated: August 13, 2026