Question 1172212
Draw this, and the equation needed from the water is h(t)=-5t^2+20t+75, the height of the cliff.
after 5 seconds, h(5)=-5*25+20(5)+75=50 m above the water.
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maximum height is at t=-b/2a or -20/-10 or 2 seconds
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it will hit the water when the equation equals 0.
changing all the signs, 5t^2-20t-75=0
there is one positive root
5(t^2-4t-15)=0
t=(1/2)(4+/- sqrt (16+60)); sqrt (76)=8.72
=6.36 seconds
{{{graph(300,300,-10,10,-25,100,50,-5x^2+20x+75)}}}