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A driver in a 1000.0 kg car traveling at 20 m/s slams on the brakes and skids to a stop. If the coefficient of friction between the tires and the   road is 0.80, how long will the skid marks be? A) 26 m B) 21 m C) 33 m D) 24 m

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Using F = ma to the direction of travel;

`-F = 1000*a`

-F is due to the reverse direction of the frictional force.

`F = 0.8*1000*9.81 = 7850 N`

 

`-7850 = 1000*a`

        `a = -7.85m/s^2`

 

Using `V^2 = U^2+2aS` to the direction of travel

`0 = 20^2+2*(-7.85)S`

`S = 25.5 m`

 

So the skid marks will be there for 25.5m `~~` 26m.

The correct answer is A).

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