Algebra.Com's Answer #849585 by ikleyn(52790)![\"\"](\"/images/stars/stars-13.gif\")  
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document.write( "A car left skid marks 16 m long when the driver brought it to a quick stop as he was traveling east.
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document.write( "Assuming the brakes decelerated the car at -15 m/s², how fast was the car traveling
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document.write( "when its brakes were first applied?
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document.write( "Standard designations:\r\n" );
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document.write( " S for the length (meters);\r\n" );
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document.write( " t for the time (seconds);\r\n" );
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document.write( " a for acceleration (deceleration) (m/s^2);\r\n" );
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document.write( " v for the speed (m/s).\r\n" );
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document.write( "Basic formulas from Physics/Mechanics/Kinematics are\r\n" );
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document.write( " S =  , (1)\r\n" );
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document.write( " a =  . (2)\r\n" );
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document.write( "These formulas are of the first row, and it is assumed that \r\n" );
document.write( "every student, who learns the subject, knows them without remainder.\r\n" );
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document.write( "We are given S and \"a\", and they want we determine \"v\".\r\n" );
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document.write( "But the basic formulas (1) and (2) do not provide direct connection between S, \"a\" and \"v\"\r\n" );
document.write( "- so, we need to derive the necessary formula from (1) and (2).\r\n" );
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document.write( "From (2), express t =  and substitute it into formula (1). You will get\r\n" );
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document.write( " S =  =  =  ,\r\n" );
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document.write( "which implies\r\n" );
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document.write( " v^2 =  , or v =  . (3)\r\n" );
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document.write( "Formula (3) is what we need. Now, to get the answer, substitute the given data in (3)\r\n" );
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document.write( " v =  =  = 21.91 m/s.\r\n" );
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document.write( "At this point, the problem is solved completely.\r\n" );
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document.write( "ANSWER. The speed of the car was 21.91 m/s when its brakes were first applied.\r\n" );
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document.write( "Solved.\r
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document.write( "Formula (3) is also the basic formula of kinematics, but it is traditionally
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document.write( "considered as the basic formula of the second row.\r
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