(10.108) Problem 4. You are investigating a rural accident. The evidene at the s
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Question
(10.108) Problem 4. You are investigating a rural accident. The evidene at the scene suggests that a car was traveling west when struck by a van traveling south. The crushed vehicles stuck together, then came to rest at the end of skid marks of length 14m along a 76° line as shown in the figure. The ground is flat with no curbs, and you estimate a coefficient of kinetic friction of 0.70 for the crushed vehicles along the path of the skid. You look up the masses of these model vehicles and find that the car is 1400 kg and the van 6500 kg. You know that the speed limit on both roads is 35 mph. Which of the drivers (if any) was speeding prior to the accident?Explanation / Answer
during skid,
a= -uk g = - 0.70 x 9.8 = - 6.86 m/s^2
vf^2 - vi^2 =2 a d
0^2 - v^2 = 2 (-6.86)(14)
v = 13.9 m/s
this was the speed just after collision.
now applying momentum conservation for collision,
1400 v1 i + 6500 v2 j = (1400 + 6500) (13.9 )(cos70i + sin70j)
along i, v1 = (1400 + 6500) (13.9) cos70 / 1400
v1 = 26.8 m/s Or 60 mph
along j , v2 = 15.9 m/s or 35.6 mph
so both were speeding.
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