# AP Physics

A car slows down from 18 m/s to rest in a distance of 91 m. What was its acceleration, assumed constant?

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1. (Vf)^2 = Vo^2 + 2ad = 0,
(18)^2 + 2a*91 = 0,
324 + 182a = 0,
182a = -324,
a = -1.78m/s^2.

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2. In coming to a stop, a car leaves skid marks 93 m long on the highway. Assuming a deceleration of 7.50 m/s2, estimate the speed of the car just before braking.

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