document.write( "Question 1168929: If an object is thrown downward with an initial velocity of 20ft/s, the distance travelled in an amount
\n" ); document.write( "of time (t) is represented by the equation s = 16t^2 + 20t. how long does it take the object to fall 40ft? (1 variable)
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Algebra.Com's Answer #793575 by ikleyn(52790)\"\" \"About 
You can put this solution on YOUR website!
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\n" ); document.write( "If an object is thrown downward with an initial velocity of 20ft/s, the distance travelled in
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\n" ); document.write( "\n" ); document.write( "The formula in your post is written incorrectly.   FATALLY  INCORRECTLY,  it is what I want to say.\r
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\n" ); document.write( "\n" ); document.write( "I observed it many times in this forum that the students / (the visitors)  write this formula incorrectly.\r
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\n" ); document.write( "\n" ); document.write( "So I prepared this text below as a standard introduction to the subject for such students / visitors.\r
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document.write( "If you have the formula for a height given to you as a function of time in the form\r\n" );
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document.write( "    h(t) = -at^2 + bt + c,    (1)\r\n" );
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document.write( "where \"a\", \"b\" and \"c\" are real numbers, a > 0, then in this formula\r\n" );
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document.write( "    (a)  the initial height is equal to the coefficient \"c\" value;\r\n" );
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document.write( "    (b)  the initial velocity is the coefficient  \"b\" in the formula;\r\n" );
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document.write( "    (c)  the coefficient \"a\" value is half of the gravity acceleration.\r\n" );
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document.write( "         For the Earth conditions, the gravity acceleration is g = 32 ft/s^2,\r\n" );
document.write( "         if you use feet for height;\r\n" );
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document.write( "         So, in this case  a = \"g%2F2\" = 16  (numerical value).\r\n" );
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document.write( "    (d)  To find the height at the time moment \"t\", simply substitute the value of \"t\" into the formula (1) and calculate.\r\n" );
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document.write( "    (e)  To find the time \"t\" when the height has a given value h = \"h%5B0%5D\", substitute  h = \"h%5B0%5D\" into equation (1)\r\n" );
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document.write( "         and solve equation  \r\n" );
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document.write( "             h(t) = -at^2 + bt + c = \"h%5B0%5D\".    (2)\r\n" );
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document.write( "    (f)  To find the time when the height is maximal, use the formula\r\n" );
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document.write( "             \"t%5Bmax%5D\" = \"b%2F%282a%29\".      (3)\r\n" );
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document.write( "    (g)  To find the maximal height, substitute the time value  t= \"t%5Bmax%5D\"  of the formula (3)  into the formula (1).\r\n" );
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\n" ); document.write( "\n" ); document.write( "To answer your questions,  use my instructions and make calculations on your own.\r
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\n" ); document.write( "\n" ); document.write( "To see numerous examples of solved problems,  look into the lessons\r
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\n" ); document.write( "\n" ); document.write( "    - Problem on a ball thrown vertically up from the top of a tower \r
\n" ); document.write( "\n" ); document.write( "    - Problem on a toy rocket launched vertically up from a tall platform\r
\n" ); document.write( "\n" ); document.write( "in this site.\r
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\n" ); document.write( "\n" ); document.write( "Consider these lessons as your textbook,  handbook,  tutorials and  (free of charge)  home teacher.
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\n" ); document.write( "\n" ); document.write( "Also,  you have this free of charge online textbook in ALGEBRA-I in this site\r
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\n" ); document.write( "\n" ); document.write( "The referred lessons are the part of this textbook under the topic \"Projectiles launched/thrown and moving vertically up and dawn\".\r
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\n" ); document.write( "\n" ); document.write( "Save the link to this online textbook together with its description\r
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\n" ); document.write( "\n" ); document.write( "Free of charge online textbook in ALGEBRA-I
\n" ); document.write( "https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson\r
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\n" ); document.write( "\n" ); document.write( "If this introduction is helpful to you,  I will be happy.\r
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\n" ); document.write( "\n" ); document.write( "If it will be not enough to you to solve the problem,  come again,\r
\n" ); document.write( "\n" ); document.write( "but with one indispensable condition:  your equation  MUST  be written correctly.\r
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\n" ); document.write( "\n" ); document.write( "Don't forget to post your  \"THANKS\"  to me for my teaching (!)\r
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