Question

Could someone answer and explain this please? Thank you!

Answer 1

Answer : option A

`P(t)= -16t^2 -88t +720`

Top of a tall boulder = 57 foot

To find the time taken for the pebble to hit the boulder

We set p(t) = 57 and solve for t

`57= -16t^2 -88t +720`

Subtract 57 on both sides

`0= -16t^2 -88t +720-57`

`0= -16t^2 -88t +663`

`0= -(16t^2 +88t -663)`

apply quadratic formula to solve for t

`t= (-b+-√(b^2-4ac))/(2a)`

plug in the values a = 16, b= 88 and c= -663

`t = (-88+-√(88^2-4(16)(-663)))/(2*16)`

`t= (-39)/(4)` and
`t= (17)/(4)`

t= -9.75 and t = 4.25

Time cannot be negative. So we ignore negative answer

the time taken for the pebble to hit the boulder is 4.25 seconds

Answer 2

Hello,

Please, see the attached file.

Thanks.