Question 81396
n 1981 Vladameir set a world record of 19ft3/4 inch for the pole vault. To reach that height he obtained a speed of approx. 36ft per second on the runway. The formula h=-16t^2+36t gives his height t seconds after leaving the ground. Use the formula to find the exact values of t for which his height was 18 ft.
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Replace h with 18 and find t:
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-16t^2 + 36t = 18
:
-16t^2 + 36t - 18 = 0; subtracted 18 from both sides, now a quadratic equation
:
Simplify, divide equation by -2
+8t^2 - 18t + 9 = 0
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Use the quadratic equation to find t: a=8; b=-18; c=9:
{{{t = (-(-18) +- sqrt( -18^2 - 4* 8 * 9 ))/(2*8) }}}
:
{{{t = (+18 +- sqrt(324 - 288 ))/(16) }}}
:
Do the math here, you should get two solutions. (0n the way up and on the way down) t = .75 sec and t = 1.5 sec