1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How to back calculate vehicle speed after crash?

  1. Nov 9, 2011 #1
    I am struggling on solving a car crash question. Could anyone help me out?

    Car 1 (C1) weighs 3,000kg, C2 weighs 12,00kg. C1 was at rest and hit by C2 from side. Both vehicles moved 4m in 1 second before total rest. In other words, C1 was pushed away from side for 4m and C2 traveled forward 10ft.

    Question: Assuming the fraction coefficient of the dry road is 0.7. What is the estimated speed of C2 before crash?

    I am not sure if I should solve this question by using Momentum (M)
    M(before)=(Mass of C1 x Velocity of C1) + (Mass of C2 x Velocity of C2)
    = (3,000 x 0) + (1,200 x V2)

    Upon crash, in the 1-second time, cars traveled 4m... so their speed after crash is 4m/s
    M (After)=(Mass of C1 x 4m/s) + (mass of C2 x 4m/s)
    =(3,000 x 4) + (1,200 x 4)

    Now if I assume M (before) = M (after)... then I can figure out initial speed V2
    But I did not use the friction here. Do I need any other factors for the calculation?

    Or should I approach this question from kinetic energy approach
    C2 was moving with kinetic energy: F2 = 0.5x (mass of C2) x (Velocity of C2)2
    C1 was at rest, so no kinetic energy.
    But I do not know how to proceed from here

    Any help is appreciated!
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted