document.write( "Question 1005463: Using the formula h=-1/2gt^2+v(0)t+h(0) (the zero in the parens is lower/small beneath the letter) and g= gravitational constant and v = upward velocity from a starting height of h.
\n" ); document.write( " 1a. What is the height after three seconds of a penny dropped from the roof of the a tall building about 1250 feet tall?
\n" ); document.write( " 1b. After how many seconds does the penny hit the ground?
\n" ); document.write( " 2. What is the height after three seconds of a ball thrown from the roof of a building about 495 feet tall and is tossed upwards with a velocity of 10m/s?
\n" ); document.write( " 2b. After how many seconds does it hit the ground?
\n" ); document.write( " Thanks in advance. I think I have the answers but want to check the work done.
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Algebra.Com's Answer #621730 by KMST(5328)\"\" \"About 
You can put this solution on YOUR website!
\"h=-%281%2F2%29gt%5E2%2Bv%5B0%5Dt%2Bh%5B0%5D\" is a general formula.
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\n" ); document.write( "For the first problem we will set:
\n" ); document.write( "\"t\"= time from the moment the penny is dropped (we will measure it in seconds, because it will be a short time),
\n" ); document.write( "\"h%5B0%5D=1250\"= height (in feet) at the moment, \"t=0\" , when the penny is dropped,
\n" ); document.write( "\"v%5B0%5D=0\"= the initial velocity (in feet/second) of the penny at \"t=0\" (since it was \"dropped\", it was not thrown up or down with any initial velocity).
\n" ); document.write( "We will use the acceleration of gravity in \"ft%2Fsecond%5E2\" , to agree with the other units:
\n" ); document.write( "\"g=32\" = acceleration of gravity in \"ft%2Fsecond%5E2\" .
\n" ); document.write( "Substituting, we get
\n" ); document.write( "\"h=-%281%2F2%2932t%5E2%2B0%2At%2B1250\"--->\"h=-16t%5E2%2B1250\"
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\n" ); document.write( "1a. For \"t=3\" , \"h=-16%2A3%5E2%2B1250=-16%2A9%2B1250=-144%2B1250=1106\" ,
\n" ); document.write( "so the height of the penny after three seconds is \"highlight%281106feet%29\" .
\n" ); document.write( "1b. When the penny hits the ground, \"h=0\" . Then,
\n" ); document.write( "\"0=-16t%5E2%2B1250\"--->\"16t%5E2=1250\"--->\"t%5E2=1250%2F16\"--->\"t%5E2=78.125\"--->\"t=sqrt%2878.125%29\"--->\"t=about+8.84\" ,
\n" ); document.write( "so the penny hits the ground after about \"highlight%288.85seconds%29\" .
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\n" ); document.write( "For the second problem we will set:
\n" ); document.write( "\"t\"= time from the moment the ball is tossed (we will measure it in seconds, because it will be a short time),
\n" ); document.write( "\"v%5B0%5D=10\"= the initial velocity (in meters/second) of the ball at \"t=0\" (since it was \"dropped\", it was not thrown up or down with any initial velocity).\r
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\n" ); document.write( "\n" ); document.write( "\"red%28IF%29\" (as I originally misread) \"h%5B0%5D=495\"= height (in meters) at the moment, \"t=0\" , when the ball is tossed,
\n" ); document.write( "We will use the acceleration of gravity in \"meters%2Fsecond%5E2\" , to agree with the other units:
\n" ); document.write( "\"g=9.8\" = acceleration of gravity in \"meters%2Fsecond%5E2\" .
\n" ); document.write( "Substituting, we get
\n" ); document.write( "\"h=-%281%2F2%299.8t%5E2%2B10t%2B495\"--->\"h=-4.9t%5E2%2B10t%2B495\"
\n" ); document.write( "2. For \"t=3\" ,
\n" ); document.write( "\"h=-4.9%2A3%5E2%2B10%2A3%2B495\"-->\"h=-4.9%2A9%2B30%2B495\"-->\"h=-44.1%2B30%2B495\"-->\"h=480.9\" ,
\n" ); document.write( "so the height of the ball after three seconds is \"highlight%28480.9meters%29\" .
\n" ); document.write( "2b. When the ball hits the ground, \"h=0\" . Then,
\n" ); document.write( "\"0=-4.9t%5E2%2B10t%2B495\" .
\n" ); document.write( "Solving the quadratic equation we get two solutions, but the negative solution does not make sense, and needs to be discarded.
\n" ); document.write( "So, \"t=%28-10+%2B+sqrt%2810%5E2-4%2A%28-4.9%29%2A495+%29%29%2F%282%2A4.9%29\"
\n" ); document.write( "\"t=%28-10+%2B+sqrt%28100%2B9702%29%29%2F9.8\"
\n" ); document.write( "\"t=%28-10+%2B+sqrt%289802%29%29%2F9.8\"
\n" ); document.write( "\"t=about%28-10+%2B+99%29%2F9.8=89%2F9.8=about9.08\" ,
\n" ); document.write( "so the ball hits the ground after about \"highlight%289.08seconds%29\" .\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"red%28IF%29\" it was really meant as \"h%5B0%5D=495\"= height (in feet),
\n" ); document.write( "we have a units mismatch.
\n" ); document.write( "We have to get everything in feet, or everything in meters.
\n" ); document.write( "Since I am a supporter of the SI system of units, I will convert \"495+feet\" to meters.
\n" ); document.write( "\"495+feet=%28495+feet%29%280.3048meters%2F%221+foot%22%29=150.9m\"(rounded), so
\n" ); document.write( "\"h%5B0%5D=150.9\"= height (in meters) at the moment, \"t=0\" , when the ball is tossed,
\n" ); document.write( "We will use the acceleration of gravity in \"meters%2Fsecond%5E2\" , to agree with the other units:
\n" ); document.write( "\"g=9.8\" = acceleration of gravity in \"meters%2Fsecond%5E2\" .
\n" ); document.write( "Substituting, we get
\n" ); document.write( "\"h=-%281%2F2%299.8t%5E2%2B10t%2B150.9\"--->\"h=-4.9t%5E2%2B10t%2B150.9\"
\n" ); document.write( "2. For \"t=3\" ,
\n" ); document.write( "\"h=-4.9%2A3%5E2%2B10%2A3%2B150.9\"-->\"h=-4.9%2A9%2B30%2B150.9\"-->\"h=-44.1%2B30%2B495\"-->\"h=136.8\" ,
\n" ); document.write( "so the height of the ball after three seconds is \"highlight%28136.8meters%29\" .
\n" ); document.write( "2b. When the ball hits the ground, \"h=0\" . Then,
\n" ); document.write( "\"0=-4.9t%5E2%2B10t%2B150.9\" .
\n" ); document.write( "Solving the quadratic equation we get two solutions, but the negative solution does not make sense, and needs to be discarded.
\n" ); document.write( "So, \"t=%28-10+%2B+sqrt%2810%5E2-4%2A%28-4.9%29%2A150.9+%29%29%2F%282%2A4.9%29\"
\n" ); document.write( "\"t=%28-10+%2B+sqrt%28100%2B2957.6%29%29%2F9.8\"
\n" ); document.write( "\"t=%28-10+%2B+sqrt%283057.6%29%29%2F9.8\"
\n" ); document.write( "\"t=about%28-10+%2B+55.30%29%2F9.8=45.30%2F9.8=about4.62\" ,
\n" ); document.write( "so the ball hits the ground after about \"highlight%284.62seconds%29\" .
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