Solving Quadratics using the Quadratic Equation

Question

A waterfall has a height of 1500 feet. A pebble is thrown upward from the top of the falls with an initial velocity of 16 feet per second. The height of the pebble h in feet after t seconds is given by the equation h=−16t^2+16t+1500. How long after the pebble is thrown will it hit the​ ground?

Answer 1

-16t^2 +16t+1500= 0

about 10 seconds to hit the ground

. graph the parabola and the x intercept looks like 10

or

use the quadratic formula

t = -16/-32 +/-(1/32)sqr(16^2 +4(16)(1500))

= about 10.195

in 10 seconds

h(10) = -16(10^2) +16(10) +1500

= -1600 +160 +1500

= 60 from the ground about to hit the ground in a fraction of a second

about 10.2 seconds to hit the ground