Average force on a 70 kg person stopped from 30 km/h over 0.3 m

Answer: average impact force = 8,101.9 N (in kilonewtons 8.102 kN, as multiples of the object's weight 11.8 × weight).

What we know

  • Mass: 70 kg
  • Impact speed: 30 km/h = 8.333333333 m/s (converted to the unit the formula takes)
  • Stopping distance: 0.3 m

Step by step

Given
m = 70 kg, v = 8.333333333 m/s, d = 0.3 m
Formula
F = m·v² / (2·d)
Substitute
F = 70 × 8.333333333² / (2 × 0.3)
Result
F = 8,101.9 N

All results

Average impact force8,101.9 N
In kilonewtons8.102 kN
As multiples of the object's weight11.8 × weight

Open the impact force calculator with these numbers → and change any of them.

The physics

When a moving object is brought to rest, its kinetic energy (½mv²) is absorbed over the stopping distance. Work equals force times distance, so the average force is the energy divided by that distance: F = ½mv² / d. The shorter the stop, the larger the force — which is the whole reason crumple zones, crash mats and packaging exist.

Standard acceleration of gravity →