document.write( "Question 1173179: (d) A ball is thrown vertically upwards from ground level with a velocity of 28 m/s
\n" ); document.write( "(i) What was its maximum height above the ground?
\n" ); document.write( "(ii) How long does it take to reach 20 m height?
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Algebra.Com's Answer #798368 by ankor@dixie-net.com(22740)\"\" \"About 
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A ball is thrown vertically upwards from ground level with a velocity of 28 m/s
\n" ); document.write( "use the formula: h = -4.9t^2 + 28t
\n" ); document.write( "(i) What was its maximum height above the ground?
\n" ); document.write( "max height occurs on the axis of symmetry. Find this using t = -b/(2a)
\n" ); document.write( "t= \"%28-28%29%2F%282%2A-4.9%29\"
\n" ); document.write( "t = 2.857 seconds to reach max height
\n" ); document.write( "Find the height at this time
\n" ); document.write( "h = -4.9*2.857^2 + 28(2.857)
\n" ); document.write( "h = -40 + 80
\n" ); document.write( "h = 40 ft max height
\n" ); document.write( ":
\n" ); document.write( "(ii) How long does it take to reach 20 m height?
\n" ); document.write( "-4.9t^2 + 28t = 20
\n" ); document.write( "-4.9t^2 + 28t - 20 = 0, a quadratic equation, use the quadratic formula
\n" ); document.write( "a=-4.9, b=28, c=-20
\n" ); document.write( "two solutions
\n" ); document.write( "t = .8368 sec on the way up
\n" ); document.write( "and
\n" ); document.write( "t = 4.8774 sec on the way down
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