[attempt?] car accident problem.

In summary: This shows that the car driver is not being truthful about the speed of the car just before the collision. In summary, the measurements and calculations show that the car driver's claim of the car's speed just before the collision is not consistent with the evidence, indicating that the driver is not being truthful.
  • #1
bby__hae!
1
0
[SOLVED] [attempt?] car accident problem.

Homework Statement


http://hypertextbook.com/physics/mechanics/momentum-two-three/accident-reconstruction-1.pdf [Broken]


Homework Equations


Pix=Pfx
Piy=Pfy
v^2 = v0^2 + 2 ax
Fk=MkN
W=mg
F=ma

The Attempt at a Solution



01.
Fk = MkN
100 N = Mk (130 N)
0.769 = Mk

car tires = 0.769 --- but then, I'm not sure of the units.


0.769 (0.7) = 0.538

truck tires = 0.538 --- again with the units.

02.
W = 13600 N
W = mg
13600 = m (9.8 m/s^2)
1387.755 kg = m

Fk = MkN
Fk = 0.769 (13600 N)
Fk = 10458.4

F = ma
10458.4 = 1387.755 a
7.536 m/s^2 = a

v^2 = v0^2 + 2 ax
0 = v0x^2 + 2 (-7.536) (8.2)
123.59 = v0x^2
11.117 m/s = speed of car


W = 69700 N
W = mg
W = 7112.245

Fk = MkN
Fk= 0.538 (69.700)
Fk = 37498.6

F = ma
37498.6 = 7112.245 a
a = -5.272 m/s^2

v^2 = v0^2 + 2 ax
0 = v0^2 + 2 (-5.272) (11)
115.984 m/s = v0^2
10.769 m/s = speed of truck

03.
Pfx=Pix --- i know i wrote the other way earlier, but I'm copying my weird notes.
(1387.755) (11.117) cos (33) + (7112.245) (10.769) cos (7) = 7112.245 v
88958.823 = 7112.245 v
v of truck = 12.508 m/s


(1387.755) (11.117) sin (33) + (7112.245) (10.769) sin (7) = 1387.755 v
17736.701 = 1387.755 v
v of car = 12.781 m/s

I asked my teacher and he said he vaguely remembering that the velocities were supposed to be 11?, but he and I couldn't find fault with the set up. I tried recalculating, and I came up with the same answer, which frustrates me a bit.

04.
As for number four, I read the facts given repeated times, but I'm still at a loss for how to approach it. I realize that I'm supposed to use parts 01.-03. though.



Thanks. :D
Sorry, it's a bit long.
 
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  • #2
The measurement of the distance between the traffic light and the collision point (d = 13.0 m) and the maximum acceleration of the car (a = 3.0 m/s^2) are not consistent with the claim of the car driver. Assuming constant acceleration, which is a pretty good assumption since the mass of the car does not change significantly as a result of the collision, we get:vf = Sqrt(2ad) = Sqrt[ 2(3.0m/s^2)(13.0 m) ] = 8.83 m/s.The percent difference between this speed and the speed of the car just before the collision calculated in question 3 is significant.% Difference = [ 12.781 m/s - 8.83 m/s ]/[ 12.781 m/s + 8.83 m/s ] x 200 = 37%.
 

1. What is the main cause of car accidents?

The main cause of car accidents is human error, including distracted driving, speeding, drunk driving, and reckless behavior.

2. How many car accidents occur each year?

According to the National Highway Traffic Safety Administration, there were approximately 6.7 million car accidents in the United States in 2018.

3. What are the most common injuries sustained in car accidents?

The most common injuries from car accidents include whiplash, broken bones, concussions, and soft tissue injuries. However, the severity of injuries can vary greatly depending on the specific accident.

4. How can car accidents be prevented?

Car accidents can be prevented by practicing safe driving habits, such as avoiding distractions, following traffic laws, and driving defensively. Regular vehicle maintenance and avoiding driving under the influence of alcohol or drugs can also help prevent accidents.

5. What should I do if I am involved in a car accident?

If you are involved in a car accident, the first step is to check for injuries and seek medical attention if necessary. Then, contact the police and exchange information with the other driver(s). It is important to document the accident and contact your insurance company to report the incident. Depending on the severity of the accident, you may also need to consult with a lawyer.

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