Arturo O. answered • 08/15/18

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v

_{f}

^{2}- v

_{i}

^{2}= 2ad

v

_{f}= final speed = 0 (full stop)

v

_{i}= initial speed = ?

d = stopping distance (given)

v

_{i}= √(-2ad)

Note that since a is negative, the argument of the square root is positive. If you do not know a but you know the braking force F and vehicle mass m, you can get a from Newton's 2nd law:

a = F/m

Anyway, we need more information to answer the question.