* At an accident scene on a level road, investigators measure a car's skid mark to be 58 m long. It was a rainy day and the coefficient of friction was estimated to be 0.38. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes.

Question

I can not figure out which formulas to use for this problem or how to solve it.

Answer 1

To answer this question you must first solve:
Acceleration=(gravity)(coefficient of friction) which equals 3.724
you than plug acceleration into the equation (velocity final)^2=(velocity initial)^2+2(acceleration)(distance)
and you solve for velocity initial:
(0)^2=(VI)^2+2(-3.724)(58)
-(VI^2)=-(431.9)
(VI^2)=431.9
VI= 20.7842 m/s
Hope that this helps

Answer 2

I have not understood where the negative came from...
how is this coming "2(acceleration)(distance)"