# Unraveling the Mystery of a Two-Car Crash

• loka
In summary: But you need v first.In summary, the conversation discusses a case where an accident occurred at an intersection with no stop signs. It involves determining whether one or both cars should be ticketed for speeding, which car had right of way, and who was at fault for the accident. The conversation also mentions using data tables and witness accounts to gather information. The problem involves finding the initial velocity of two cars of different masses that were skidding together and stopping at a certain distance. The coefficient of friction and the rules of the road are also mentioned. Various equations and principles are suggested for solving the problem.
loka

## Homework Statement

On May 19, an accident occurred at the corner of two asphalt streets with no stop signs. The speed limit was 40 km/h on both streets. As lead CSI on the case, you must determine whether one or both cars should be ticketed for speeding, which car had right of way at the intersection, and whether one driver or both were at fault for the accident.

Using data tables, you have determined that the mass of car A is 2275 kg and the mass of car B is 1525 kg. You measured the skid marks when the cars were locked together and found that they were 3.705 m long at an angle of 47 degrees east of the northbound street. Witness accounts put both cars 5 m from the intersection at the same time. The coefficient of kinetic friction b/w rubber and asphalt is 0.80. The rules of the road at an intersection w/o stop signs is that if 2 cars get to the intersection at the same time, the right-hand car has right of way.

Please see sketch.

J = F (t)

p = mv

## The Attempt at a Solution

...I'm really at a lost of what to do...

Last edited:
Hi there,

I can't open you image.

Cheers

Think about the motion of the two cars joined together - treat this as a single object which moves in the direction and distance that is stated in the problem. What forces are acting on this object? It is moving with a certain velocity v, then it moves 3.705m, and final velocity is 0 when it's stopped. What can you do to find the initial veloctiy of the object (the two cars)? What principle will help you when you have this value v?

u=initial velocity
v=final velocity
A=1
B=2

Given:

M1 = 2275 kg
M2 = 1525 kg
d = 3.705 m
angle = 47 deg
coeff. of friction = 0.80

----
Q1: Is the final velocity when it stopped or during the 'skidding time'? But one thing is for sure...it's the same for both of them and it's slower than the initial...

so... v1 = v2
----

Q2: Does the 5m distance from the intersection have any relevance to the calculations? Or is it just there to tell us that they were at the same distance from the intersection at the same time?
----

Find:
u1 = ?
u2 = ?

...once found, I can compare it to the speed limit? ... right?

Random Ideas on how to start it...

A. $$\sum$$p1 = $$\sum$$p2
m1u1 + m2u2 = (m1 + m2) v
??

B. Forces at an angle? so...and somehow incorporate $$\mu$$?
Fny = Fg

Q1: Is the final velocity when it stopped or during the 'skidding time'? But one thing is for sure...it's the same for both of them and it's slower than the initial...

Think of this problem in two parts, you're already going along the right lines. Take the second part of the problem first. An object (here two cars together) of mass m1 and m2 moves with an initial velocity v. This is what you need to find. For this motion, you know the mass of the object and the distance it takes to slow from v to 0 (ie, it stops). What net force is acting on the object? In what direction? How can you use Newton's Laws to find a, the deceleration on the object, and then find v?

A. LaTeX Code: \\sum p1 = LaTeX Code: \\sum p2
m1u1 + m2u2 = (m1 + m2) v
??

Yes, once you have the combined v, you can then return to conservation of momentum immediately before and after the collision.

## What is a two-car crash?

A two-car crash, also known as a two-vehicle crash, is a type of traffic collision where two cars are involved. This can occur on any type of road or intersection and can have varying levels of severity.

## How do two-car crashes happen?

Two-car crashes can happen for a variety of reasons, including driver error, mechanical failures, road conditions, and external factors such as weather or animals. They can also occur due to a combination of these factors.

## What are the common injuries in a two-car crash?

The most common injuries in a two-car crash are whiplash, cuts and bruises, broken bones, and head injuries. However, the severity of injuries can vary greatly depending on the circumstances of the crash. In some cases, car occupants may also suffer from more serious injuries such as spinal cord injuries or traumatic brain injuries.

## What should I do if I am involved in a two-car crash?

If you are involved in a two-car crash, the first step is to ensure your safety and the safety of others involved. This may include moving to a safe location, calling emergency services, and exchanging information with the other driver. It is also important to seek medical attention and document any injuries or damages for insurance purposes.

## How can scientists help unravel the mystery of a two-car crash?

Scientists can use various methods such as crash reconstruction, data analysis, and simulation to study and understand the factors that contribute to a two-car crash. They can also develop safety measures and technologies to prevent or reduce the severity of these crashes. Additionally, scientists can work with policymakers to implement regulations and laws that promote safer driving practices.

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