- #1
Abarak
- 28
- 0
Homework Statement
You are called as an expert witness to analyze the following auto accident: Car B, of mass 2100 [tex]kg[/tex], was stopped at a red light when it was hit from behind by car A, of mass 1400 [tex]kg[/tex]. The cars locked bumpers during the collision and slid to a stop. Measurements of the skid marks left by the tires showed them to be 7.25 [tex] m [/tex] long, and inspection of the tire tread revealed that the coefficient of kinetic friction between the tires and the road was 0.650.
What was the speed ([tex] v [/tex]) of car A ([tex]mph[/tex]) just before the collision?
By how many [tex]mph[/tex] was car A exceeding the speed limit 35.0 [tex]mph[/tex]?
Homework Equations
I have tried
1.) [tex]m_1 v_1i + m_2 v_2i = (m_1+m_2)v_f[/tex] (does not work)
2.) [tex]v_f^2-v_o^2=2-U_k(g)D[/tex] (does not work)
The Attempt at a Solution
The first equation above I know will not work because it was designed for a perfect inelastic collision. I need to take into account the friction, that is why I used equation two.
[tex]v_f^2-v_o^2=2-U_k(g)D[/tex]
[tex]v_f = 0 m/s[/tex]
[tex]v_0 = ?[/tex] (need to find for problem #1)
[tex]U_k = 0.650[/tex]
[tex]g = 9.8 m/s^2[/tex]
[tex]D = 7.25m[/tex]
Any ideas to what I could be doing wrong?