Question 1131410
{{{ h = -4.9t^2 + 4t + 3 }}}
{{{ h = 3.5 }}}
{{{ 3.5 = -4.9t^2 + 4t + 3 }}}
{{{ -4.9t^2 + 4t - .5 = 0 }}}
{{{ t = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
{{{ a = -4.9 }}}
{{{ b = 4 }}}
{{{ c = -.5 }}}
{{{ t = (-4 +- sqrt( 4^2-4*(-4.9)*(-.5) ))/(2*(-4.9)) }}}
{{{ t = (-4 +- sqrt( 16 - 9.8 ))/((-9.8)) }}}
{{{ t = ( -4 +- sqrt( 6.2 ) )/(-9.8) ) }}}
{{{ t = ( -4 + 2.49 )/(-9.8) }}}
{{{ t = (-1.51)/(-9.8) }}}
{{{ t = .154 }}}
and, also:
{{{ t = ( -4 - 2.49 )/(-9.8) }}}
{{{ t = .662 }}}
The height is greater than 3.5 m above the water
between .154 sec and .662 sec
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Here's the plot:
{{{ graph( 400, 400, -2, 2, -1, 4, -4.9x^2 + 4x + 3 ) }}}
Looks like the answers could be right. Check the math.