How to Calculate the Speed When Two Cars Collide?

[Cox]

Select the ground as the reference frame and the direction of Car A as the positive direction. The speed of Car A is 60 kilometers per hour, and the speed of Car B is 6 kilometers per hour, so the speed difference between them is 120 kilometers per hour.

[DiHannah]

I used to study some physics, and recalling how to calculate the speed during a collision between two cars is quite interesting. The key lies in the principle of momentum conservation. Simply put, the total momentum before the collision equals the total momentum after. The formula is m1v1 + m2v2 = m1v1' + m2v2', where m is the mass of the car, v is the speed, and v' is the speed after the collision. To calculate it precisely, you need to know the masses of both cars, the angle of collision, and the extent of deformation. For example, in a head-on collision, the speed change is significant, making the calculation more complex; in a side collision, the angle deviation must be considered. In practice, engineers use simulation software to model these data, combined with on-site measurements to derive values. But safety comes first—if an accident occurs, don't speculate on your own; seek expert help immediately, as speed calculation is crucial for determining liability. When driving, always maintain a safe distance, avoid sudden braking, and minimize collision risks.

[FranciscoRose]

I once witnessed a car accident investigation firsthand, where professionals meticulously measured the length of skid marks at the scene to estimate speed. For example, if a car braked sharply from 50 mph to the point of collision with 20 meters of skid marks, they could use the formula: speed = square root (2 * friction coefficient * gravitational acceleration * braking distance) to calculate the initial speed. The friction coefficient depends on the road surface, with lower values for slippery conditions. The speed change at the moment of impact also considers the collision angle—head-on collisions lose more energy, while oblique impacts may have greater deviations. Damage assessment is also crucial; deeper front-end deformation indicates higher speed. It's best to preserve evidence like dashcam footage to aid in accurate calculations. In short, leave this to the police or forensic experts to avoid errors affecting claims. Safe driving is paramount—don't speed.

[HarrisonRose]

After a minor car scrape, I usually try to estimate the speeds involved. I recall my speed and the other vehicle's speed. For example, if I was driving at 40 km/h and the other party was roughly at 60 km/h, with the impact point closer to my front bumper, my speed might have been absorbed. Vehicle data recorders or mobile GPS can serve as references. For more precise calculations, heavier vehicles experience less speed variation; greater damage indicates higher speed. Don't rely too much on subjective feelings as the margin of error is large—it's best to report to insurance promptly. Speed estimation plays a crucial role in accident handling.