What is a perfectly inelastic collision?

A perfectly inelastic collision is one where the two objects stick together after impact and move as a single combined mass. Momentum is conserved, but the maximum possible kinetic energy is lost.

Is momentum conserved in this type of collision?

Yes. The total momentum before and after the collision is identical. Only kinetic energy is not fully conserved — some is converted to internal energy (heat, sound, deformation).

Can I use negative velocities?

Yes. Negative velocity indicates motion in the opposite direction (leftward by convention). For example, enter -5 m/s for an object moving left at 5 m/s.

What does zero post-collision velocity mean?

It means the two objects had equal and opposite momenta, so the combined system comes to a complete stop. All initial kinetic energy is lost.

What units does this calculator use?

Mass is in kilograms (kg), velocity in meters per second (m/s), momentum in kg·m/s, and energy in joules (J).

How is energy loss calculated?

Energy loss = KE_initial - KE_final = (0.5*m1*v1² + 0.5*m2*v2²) - 0.5*(m1+m2)*vf². A positive value means energy was dissipated; zero would indicate a perfectly elastic collision (not this tool).

Inelastic Collision Calculator

Enter the masses and initial velocities of two objects to find the post-collision velocity and kinetic energy lost in a perfectly inelastic collision.

Object Parameters

1 Object 1

Mass (kg)

Velocity (m/s)

2 Object 2

Mass (kg)

Velocity (m/s)

Results

Enter values and press Calculate

Collision Diagram

Before

m₁

m₂

→

After

m₁+m₂

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Summary

This tool applies conservation of momentum to perfectly inelastic collisions, where two objects stick together after impact. Enter the mass and initial velocity of each object to instantly calculate the shared post-collision velocity, total momentum, initial and final kinetic energies, and the energy dissipated as heat, sound, or deformation. Positive velocities move right; negative velocities move left.

How it works

Enter the mass of object 1 (kg) and its initial velocity (m/s). Use a negative value for leftward motion.
Enter the mass of object 2 (kg) and its initial velocity (m/s).
The calculator applies p = m1*v1 + m2*v2 to find total momentum.
Post-collision velocity is derived as v_f = (m1*v1 + m2*v2) / (m1 + m2).
Initial and final kinetic energies are computed; the difference is the energy lost.
Click Calculate or press Enter to generate the results and updated diagram instantly.

Use cases

Physics homework and exam preparation on momentum and collisions.
Verifying lab results for collision experiments.
Estimating energy dissipated in car crash simulations.
Understanding how mass ratio affects post-collision velocity.
Teaching conservation of momentum interactively.
Engineering analysis of impact and shock absorption.

Frequently Asked Questions

Last updated: 2026-06-13 · Reviewed by Nham Vu