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

[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!

 

[PeroK]

It depends what the wall is made of.

 

[Halc]

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.

 

[nirgro]

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?

 

[PeroK]

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!

 

[phinds]

isnt it like a car hit a wall at 60?

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.

 

[nirgro]

why?

 

[PeroK]

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.

 

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.

 

[phinds]

why?

Why WHAT? Which statement are you questioning?

 

[nirgro]

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.

 

[Mister T]

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.