WEBVTT

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Here is the problem: A car moving at 30 m/s brakes at 6 m/s squared until it stops. Find the stopping distance and time.

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Find displacement s and time t for motion in a straight line with constant acceleration.

3
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List the known quantities. Unknown: displacement s and time t.

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Time.

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Displacement.

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So the answer is s equals 75 m, t equals 5 s.

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With constant acceleration, any three of displacement, initial velocity, final velocity, acceleration and time fix the other two. Each pair of unknowns is solved with the equation that does not contain the other unknown.

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Check v squared equals u squared plus 2as: 0 equals 0.