What is the true impact speed when two cars collide head-on at 50mph?

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In summary, the impact speed in a head-on collision between two identical vehicles traveling at 50mph is 50mph. This is because each vehicle is going through a transition of 50mph down to 0mph in the space of a crumple zone. However, it can also be argued that the impact speed is 100mph if looking at the frame of reference of one of the vehicles, as the other vehicle is approaching at 100mph. The term "impact speed" is open to interpretation and can depend on the frame of reference. The amount of energy involved in the impact is the same regardless of the reference frame, but the force and duration of the impact may vary. In a head-on collision with a stationary wall,
  • #36
torquil said:
According to the sources I've seen: for a given road, a lower speed limit leads to fewer deaths and less emissions.

Why? Less kinetic energy involved and less energy dissipation per unit distance.

However, it could be argued that since cars have a lower fuel efficiency at lower speeds it is likely that more HARMFUL Carbon Monoxide might be released.
 
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  • #37
elemis said:
However, it could be argued that since cars have a lower fuel efficiency at lower speeds it is likely that more HARMFUL Carbon Monoxide might be released.

If I can drive the same car at either 100km/h or 80km/h on different gears at the same engine RPM, it's pretty obvious which speed is more efficient, even per unit distance. This happens because everything is approximately the same within the car, apart from the much larger air resistance...

I think that considerations about engine efficiency vs RPM (which shouldn't cause very much difference anyway since cars have gear boxes), are second order effects that cannot "compete" with the unavoidable increase in energy dissipation caused by the rapidly increasing air resistance as speed is increased (unfortunately, it increases more rapidly than v to the first power...)

There is no question that a car with a gear box and a combustion engine, if constructed to do so, will be more efficient (less energy loss per unit distance) e.g. at 80km/h than at 100km/h.

Unfortunately, as interesting as this discussion is, I guess it belongs in a different thread.
 
<h2>1. What factors affect the impact speed in a head-on car collision?</h2><p>The impact speed in a head-on car collision is affected by several factors, including the weight and speed of the vehicles, the angle of impact, and the presence of safety features such as airbags and seatbelts.</p><h2>2. Is the impact speed always equal to the combined speed of the two vehicles?</h2><p>No, the impact speed is not always equal to the combined speed of the two vehicles. In a head-on collision, the impact speed is actually lower than the combined speed due to the force of the impact being distributed between the two vehicles.</p><h2>3. How does the impact speed affect the severity of injuries in a head-on collision?</h2><p>The impact speed is a major factor in determining the severity of injuries in a head-on collision. The higher the impact speed, the greater the force of the impact and the more severe the injuries are likely to be.</p><h2>4. Can the impact speed be accurately calculated in a real-world head-on collision?</h2><p>In a real-world head-on collision, the impact speed can be difficult to accurately calculate due to the complex physics involved. However, accident reconstruction experts can use various techniques and data to estimate the impact speed.</p><h2>5. How can the impact speed in head-on collisions be reduced?</h2><p>The impact speed in head-on collisions can be reduced by implementing safety measures such as speed limits, traffic signals, and barriers on roads. Additionally, using safety features in vehicles, such as airbags and seatbelts, can also help reduce the impact speed and severity of injuries in a collision.</p>

1. What factors affect the impact speed in a head-on car collision?

The impact speed in a head-on car collision is affected by several factors, including the weight and speed of the vehicles, the angle of impact, and the presence of safety features such as airbags and seatbelts.

2. Is the impact speed always equal to the combined speed of the two vehicles?

No, the impact speed is not always equal to the combined speed of the two vehicles. In a head-on collision, the impact speed is actually lower than the combined speed due to the force of the impact being distributed between the two vehicles.

3. How does the impact speed affect the severity of injuries in a head-on collision?

The impact speed is a major factor in determining the severity of injuries in a head-on collision. The higher the impact speed, the greater the force of the impact and the more severe the injuries are likely to be.

4. Can the impact speed be accurately calculated in a real-world head-on collision?

In a real-world head-on collision, the impact speed can be difficult to accurately calculate due to the complex physics involved. However, accident reconstruction experts can use various techniques and data to estimate the impact speed.

5. How can the impact speed in head-on collisions be reduced?

The impact speed in head-on collisions can be reduced by implementing safety measures such as speed limits, traffic signals, and barriers on roads. Additionally, using safety features in vehicles, such as airbags and seatbelts, can also help reduce the impact speed and severity of injuries in a collision.

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