how long after the pebble is thrown will it hit the ground

Question

Height of 1500ft pebble thrown upward initial velocity of 20ft per second the height h of pebble after the seconds is given the equation h=-16t2+20t+1500

Answer 1

vi=20'/sec

up "t" = v_i / g

20/32.2=.621/sec

distance up="d"=½gt²

^{(.621^2)/2=.19289.....}

^{+1500=1500.193}

^{Gravity= ((t^2*t)/2)32.2=1500.193}

^t=<9.1659sec

Answer 2

I plugged this equation into the TI-84 calculator and looked for the x intercept using CALC-Zero funtion. I found t=10.33 seconds

To do this manually, you plug in h=0 (height is zero when it hits the ground) and use the quadratic equation to solve.

a=-1, b=20 and c=1500

Throw out the negative solution, time can't be negative.