A car skidded on a roadway that has a coefficient of friction with the road of 0.7. A police officer measured the skid marks and noted them to be 100 feet long. Two years later at trial, the lawyer for the driver argues that the officer did not measure the skid marks correctly. He asserts, based on photographs, that skid marks were no more than 92 feet long. Is the difference significant?

Question

A car skidded on a roadway that has a coefficient of friction with the road of 0.7.  A police officer measured the skid marks and noted them to be 100 feet long.  Two years later at trial, the lawyer for the driver argues that the officer did not measure the skid marks correctly.  He asserts, based on photographs, that skid marks were no more than 92 feet long.  Is the difference significant?

bobpursley · Answer

Assuming the car came to a stop..

vf^2=vi^2+ 2ad=vi^2 - 2 mu*g*d

vi=sqrt (2mu*g*d)

so the question is what is the ratio of
sqrt(92/100)?

well, at 92, vi kwould have been 96 percent of what the officer orginally estimated. Probably not significant.