Question

H=255-21t-16t^2

PLEASE HELP!!

Answer 1

3.15 seconds is the answer.

Step-by-step explanation

when the ball touches the ground, h =0

hence,

0=255-21t-16t²

16t²+21t-225=0

here a=16 ,b=21, c= -225

`t= \frac{ - b± \sqrt{ {b }^(2) - 4ac} }{2a} \\ \\ t= \frac{ - 21± \sqrt{ {21}^(2) - 4 * 16 * - 225} }{2 * 16} \\ = ( - 21 ± √(441 - ( - 14400)) )/(32) \\ = ( - 21± √(14841) )/(32) \\ = ( - 21±121.82)/(32) \\ \\ t = ( - 21 + 121.82)/(32) \: or \: \: t = ( - 21 - 121.82)/(32) \\ t = 3.15 \: \: or \: \: t = - 4.46`

time cannot be negative, hence t = -4.46 can be avoided

The ball takes 3.15 seconds to hit the ground.