# Help please with a physics bet (2 cars colliding vs. 1 car hitting a wall)

• nirgro
In summary, two cars with the same mass will experience the same impact when colliding with each other at 30 mph, which is equivalent to hitting an immovable wall at 15 mph. If the cars are moving in opposite directions, the impact is equivalent to hitting the wall at 30 mph. The extent of damage depends on the crumple characteristics of the car and the kinetic energy lost in the collision. Ultimately, the speed at which a car needs to hit a wall in order to have the same impact as a collision with another car depends on the wall's material and the time it takes for the car to come to a complete stop.
nirgro
so the question is this.

2 cars with the same mass hits each other at the speed of 30 miles.
at which speed a car needs to hit a wall in order to get set same impect?
i don't care what Will hurt the driver more.

thanks!

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It depends what the wall is made of.

I assume the cars hit head on. I cannot see the attachment.

Two cars with a relative speed of 30 mph (I assume you mean mph and not miles) will each receive about the same impact (same short-duration change in velocity, same damage) as hitting a stationary immovable wall at 15 mph.

If on the other hand the cars are each moving at 30 mph in opposite directions (a relative speed of 60 mph), then they will each receive about the same impact as hitting the wall at 30 mph.

Dale
sorry not sure i got what you say
2 cars hit each other at the speed of 30 each one of them.its like one car hits the wall at 15??
isnt it like a car hit a wall at 60?

Last edited by a moderator:
nirgro said:
sorry not sure i got what u say
2 cars hit each other at the speed of 30 each one of them.its like one car hits the wall at 15??
isnt it like a car hit a wall at 60?
You might be losing this bet!

etotheipi
nirgro said:
isnt it like a car hit a wall at 60?
PeroK said:
It depends what the wall is made of.

It also depends on the crumple characteristics of the car. Your question is way too vague to have a solid answer.

why?

nirgro said:
why?
If the wall is unbreakable and immovable, then hitting it at 30mph is the same as two cars hitting each other if both are doing 30mph. The impact on the car is the same: it stops dead from 30mph to zero with no forward motion.

hutchphd and berkeman
Extent of deformation of the car relates to the kinetic energy lost in the collision. If one car, initially with ##v_0 = 15\text{mph}##, hits a wall, then it gets ##\frac{1}{2}m{v_0}^2## worth of deformation.

If two cars, each with ##v_0 = 15\text{mph}## (i.e. approach speed ##2v_0 = 30\text{mph}##) hit each other, then each is still apportioned ##\frac{1}{2}m{v_0}^2## worth of deformation. This assuming symmetry, of course.

nirgro said:
why?
Why WHAT? Which statement are you questioning?

ok thanks a lot friend i get it so the answer is like hiting the wall at 30.
so i lost the bet but still nice to know

thanks.

hutchphd and PeroK
If the car's speed changes from 30 mi/h to zero, it doesn't matter whether that happens because of a collision with a wall or with another car. What does matter is the time it takes the car to make that change in speed. The larger the time the smaller the acceleration and hence the smaller the damage.

Usually in a question like this we assume the time taken is the same in both cases, or at least about the same, so that it makes no difference. The damage is the same in both cases.

## 1. What factors affect the outcome of a collision between two cars?

The outcome of a collision between two cars is affected by several factors, including the speed and mass of the cars, the angle of impact, and the presence of safety features such as airbags and seat belts. The type of collision, whether it is head-on, rear-end, or side impact, also plays a significant role in determining the outcome.

## 2. How does the force of impact differ between a collision between two cars and a car hitting a wall?

In a collision between two cars, the force of impact is shared between the two vehicles, as they both exert a force on each other. In contrast, when a car hits a wall, the force of impact is absorbed entirely by the car, resulting in a higher force and potentially more damage.

## 3. Can the outcome of a collision be predicted?

While it is possible to make predictions based on the factors mentioned above, the outcome of a collision is ultimately unpredictable. The behavior of the vehicles and the forces involved can vary greatly depending on the specific circumstances of the collision.

## 4. How do safety features affect the outcome of a collision?

Safety features such as airbags and seat belts are designed to reduce the impact forces on the occupants of a vehicle during a collision. They can significantly decrease the likelihood of serious injuries or fatalities in a collision.

## 5. Is there a way to minimize the damage in a collision?

While it is not possible to completely eliminate the damage in a collision, there are steps that can be taken to minimize it. These include driving at safe speeds, maintaining a safe distance from other vehicles, and ensuring that safety features are in good working condition.

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