Question

Two cars that have the same mass and velocity have a head on collision. A car with the same mass and velocity as the first situation crashes into a massive wall. which has more damage?

Answer 1

When something is damaged, it's often because it could not withstand the energy transfered to it, either because of the high amount, or the way it was transfered. For an electric circuit (or a computer), it can be electric energy (power surge) or physical (a hammer and an angry person).
Therefore, if the car is damaged, it's because of the enormous amount of energy that was transfered to it. (I won't get into the other details about fractures, energy dispersion and conversion, but just know that what I've said is not all there is to it, it's just enough for this situation).
Now, which collision has more energy put into it? knowing that
\[K_{e}=\frac{ 1 }{ 2 } mv ^{2}\]
and you have 2 objects colliding and sharing the impact in both situation?

Answer 2

the first situation has more energy going into it

Answer 3

exact. because no matter the mass of the wall, it doesn't have any speed, so no kinetic energy.

Answer 4

In the first situation, there will be more damage done to the car

Answer 5

which ever loses more kinetic energy has the most damage correct?

Answer 6

Very roughly, yes.

Answer 7

but if your car was made of rubber, all the energy would be absorbed...
which is not the case now, I just want you to know that though

Answer 8

everywhere i looked it says that the two crashes have the same amount of damage

Answer 9

What course is it?

Answer 10

college physics

Answer 11

The total amount of energy in this system is found by using the kinetic energy equation (KE = ½ mv2). So KE = (2)(1/2 mass)(v2). The KE equation is multiplied by two because there are two cars in the system with equal values of m and v. This equals the same total amount of energy as the car and wall collision, meaning that neither collision did more damage. There was the same amount of damage in both systems.

Answer 12

but for the wall the wall would have zero final velocity correct? canceling its KE?

Answer 13

I don't know what they assumed when they wrote this, but when organizations do collision tests with cars, they throw a car at 64kph at a wall, to simulate a crash between two cars at 50kph.

Answer 14

yes, 0 initial and 0 final, but still energy will be transfered to it, in the form of internal energy (brick nods will be crushed closer together, building up tension, which requires more energy to sustain) and heat will be evacuated

Answer 15

im gettin that the first situation will have twice as much damage than the second but everyone is saying im wrong and they are equal

Answer 16

I guess... for the sake of your exam, believe it. When you get to university, find another answer.

Answer 17

i wish i took university instead ive already had calculus

Answer 18

It's the same thing as saying in high school that a block that is pushed will keep on moving forever, because there's no friction. It's a simplification.
But this one about the cars is so widespread that even teachers will sometime believe if they haven't studied it.

Answer 19

ohh, that's right, in US it's either college or university, I forgot

Answer 20

yea thats how it is here