contestada

The height, h, in feet of a ball above the ground is given by h= -16t^2+64t+80, where t is the time in seconds. How long does it take the ball to hit the ground?

A) 3 seconds
B) 4 seconds
C) 5 seconds
D) 6 seconds

Respuesta :

Sriju

Answer:

It is 5 seconds     option C

Step-by-step explanation:

When the ball would hit the ground, h would reduce 0.

We can equate the R.H.S to 0.

∴ 0= -16t²+64t+80

0 = t² - 4t - 5              (dividing both sides by -16)

0 = t²+t - 5t -5  (by splitting the middle term)

0 = t ( t+1) -5 (t+1)

0= (t-5) * (t + 1)

when t-5=0   ;   when t+1=0

t =5           ;          t= -1                    time cannot be -ve

∴ t= 5 seconds

Hope this helps you.