Calculate momentum (p = mv), impulse (J = FΔt = Δp) and the result of a perfectly inelastic collision, where two objects stick together. Leave one value empty and this free calculator solves for it, using conservation of momentum.
Momentum formulas
Worked example
A 1,500 kg car at 20 m/s hits a stationary 1,000 kg car and they lock together. Momentum before = 1500 × 20 = 30,000 kg·m/s, so v = 30,000 ÷ 2,500 = 12 m/s. Kinetic energy falls from 300 kJ to 180 kJ: 40% is lost to deformation, heat and sound, but momentum is conserved.
A 160 g cricket ball turned around from 40 m/s to −20 m/s in 5 ms has Δv = 60 m/s, so the bat exerts an average force of 0.16 × 60 ÷ 0.005 = 1,920 N.
Frequently asked questions
How do you calculate momentum?
Multiply mass by velocity: p = mv. A 0.16 kg ball at 40 m/s has a momentum of 6.4 kg·m/s.
What is impulse?
Impulse is force multiplied by the time it acts (FΔt), and it equals the change in momentum. Its unit is N·s, which is the same as kg·m/s.
Is momentum conserved in a collision?
Yes, total momentum is conserved in every collision as long as no external force acts. Kinetic energy is only conserved in perfectly elastic collisions.
Why do I enter negative velocities?
Momentum is a vector. Pick one direction as positive; anything moving the other way gets a negative velocity.
Related tools
Free educational tool by HawkInc. Results are calculated in your browser and rounded for display; check critical work by hand or with a second method.