document.write( "Question 1113068: A ball is thrown vertically upwards from the top of a school building. It’s height, h metres, above the ground, can be modelled by h=18+6t-4t^2, where t is the time in seconds after it leaves the top of the building.
\n" ); document.write( "i) how tall is the school building?
\n" ); document.write( "ii) at what time will the ball strike the ground? \n" ); document.write( "

Algebra.Com's Answer #728118 by ikleyn(52781) $\"\"$ $\"About$

You can put this solution on YOUR website!
.
\n" ); document.write( "

\r\n" );
document.write( "The correct equation written for the Earth conditions, must have coefficient EITHER -4.9 at t^2,  OR -5,\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "depending on which value of the gravity acceleration,  9.81 m/s^2   or simply rounded 10 m/s^2 is used.\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "Simply speaking,  your equation is written incorrectly,\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "so further discussion makes no sense.\r\n" );
document.write( "

\r
\n" ); document.write( "\n" ); document.write( "==============\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Let me explain you EVERYTHING about these problems,
\n" ); document.write( "from the very beginning to as far as you need to know it NOW.\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "

\r\n" );
document.write( "    You may often meet these problems on a projectile thrown vertically upward.\r\n" );
document.write( "\r\n" );
document.write( "    The equation for the height over the ground usually has ONE OF TWO POSSIBLE forms:\r\n" );
document.write( "\r\n" );
document.write( "        a)  h(t) = -16*t^2 + v*t + c\r\n" );
document.write( "\r\n" );
document.write( "                 In this form, the equation is written for the height h(t) over the ground measured in feet.\r\n" );
document.write( "                 The value of \"16\" is the half of the value of the gravity acceleration g = 32 ft/s^2.\r\n" );
document.write( "\r\n" );
document.write( "                 The sign \"-\" at the first term means that the gravity acceleration is directed down, \r\n" );
document.write( "                 while the \"y\"-axis of the coordinate system is directed vertically up, in the opposite direction.\r\n" );
document.write( "\r\n" );
document.write( "                 The value of \"v\" in this equation is the value of the initial vertical velocity. \r\n" );
document.write( "\r\n" );
document.write( "                 The value of \"c\" is the initial height over the ground.\r\n" );
document.write( "\r\n" );
document.write( "                 The ground level is assumed to be 0 (zero, ZERO). In other words, the origin of the coordinate system is at the ground.\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "        b)  h(t) = -5*t^2 + v*t + c\r\n" );
document.write( "\r\n" );
document.write( "                 It is another form of the \"height\" equation for the same process.\r\n" );
document.write( "\r\n" );
document.write( "                 In this form, the height h(t) is measured in meters (instead of feet).\r\n" );
document.write( "\r\n" );
document.write( "                 The value of \"5\" at the first term is the same gravity acceleration, but this time expressed in \"m/s^2\" units\" g = 10 m/s^2.\r\n" );
document.write( "\r\n" );
document.write( "                       Actually, more precise value is g = 9.8 m/s^2, therefore, sometimes, this equation goes with the first term -4.9.\r\n" );
document.write( "\r\n" );
document.write( "                 The value of \"v\" is the vertical velocity, expressed in m/s.\r\n" );
document.write( "\r\n" );
document.write( "                 The value of \"c\" is the initial height over the ground in meters.\r\n" );
document.write( "

\r
\n" ); document.write( "\n" ); document.write( "==============\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "In this site, there is a bunch of lessons on a projectile thrown/shot/launched vertically up\r
\n" ); document.write( "\n" ); document.write( "    - Problem on a projectile moving vertically up and down\r
\n" ); document.write( "\n" ); document.write( "    - Problem on an arrow shot vertically upward\r
\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( "\n" ); document.write( "Also, you have this free of charge online textbook in ALGEBRA-I in this site\r
\n" ); document.write( "\n" ); document.write( "    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.\r
\n" ); document.write( "
\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
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Save the link to this online textbook together with its description\r
\n" ); document.write( "
\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
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "to your archive and use it when it is needed.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "

\n" );