(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

The Known Facts of the Accident

[1] Ned was traveling North on Oak Avenue in his car of mass 2000kg

[2] Ed was traveling East on King Street in his truck of mass 3000 kg

[3] The two approached the intersection at the same moment.

[4] With his stoplight “green”, Ned had the right-of-way and entered the intersection.

[5] Ed admitted that he failed to stop for the light and entered the intersection at the same moment as Ned.

[6] The collision occurred in the middle of the intersection.

[7] Both cars locked together upon impact and slid to a stop.

[8] From the point of impact (determined by shattered headlights on the pavement), the cars traveled a distance of 6.0 meters along a line that measured 40o North of East.

[9] From data tables in their accident investigation manuals, the investigators determined that the coefficient of friction between the road and the sliding cars was 1.5

Questions to Be Answered

[A] Considering the road surface to be horizontal, what was the frictional force that acted upon the locked sliding cars to stop them?

What was the magnitude of the acceleration that this force produced on the sliding cars sliding together?

[C] Based upon the stopping distance from the point of impact and the acceleration, what was the speed of the two locked cars at the moment after the impact?

[D] What was the momentum of the two locked cars at the moment after the impact?

[E] What part of this momentum did Ed contribute? (this would be his momentum before impact)

[F] What part of this momentum did Ned contribute?

[G] What was Ed’s speed before the collision?

[H] What was Ned’s speed before collision?

The speed limit at the intersection was 35 mi/hr. The police will ticket drivers for speeding if they exceeded the speed limit by more than 5 mi/hr. Should either of the two drivers be ticketed for speeding? Defend your answer with calculations.

2. Relevant equations

3. The attempt at a solution

So these are the questions I've already got to:

My Work:

A) To find the friction force I used this formula: Ff = coefficient of friction x mass x 9.81

So my friction force came out to be 73575 N which turned into 70,000 N because of significant numbers.

B) F = m x a so 70000 = 5000a and a = 14 m/s/s

C) vf^2 = vi^2 + 2ad

vf^2 - vi^2 = 2ad

vf^2 = 2 x (14)(6)

vf^2 = 168

vf = 12.96

vf = 13 m/s

D) Momentum: P = m x v

P = (2000 + 3000) kg x (13 m/s)

P = 65000 kg m/s

E) Momentum of Ed: P = m x v

P = 3000 kg x 13 m/s

Ed: P = 39000 kg m/s

F) Momentum of Ned: P = m x v

P = 2000 kg x 13 m/s

Ned: P = 26000 kg m/s

I just don't know how to find their initial speed!?!?!?!

And I feel like I didn't do E and F right.

Please someone help!!!!

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Finding Speed Before Crash?

**Physics Forums | Science Articles, Homework Help, Discussion**