Question

Posting a screenshot, help pls.

Answer 1

when h=0, that is when it hits the ground

0=70-4t-16t²
based on your previous questions, you should have learned how to complete the square

solve by copmleting the square

minus 70 both sides
-70=-4t-16t²
times both sides by -1
70=4t+16t²
16t²+4t=70
divide both sides by 16
t²+1/4t=35/8
take 1/2 of the linear coefint and square it
half of 1/4=1/8, (1/8)²=1/64
add that to both sides
t²+1/4t+1/64=35/8+1/64
factor perfect square trionomial

`(t+(1)/(8))^2=(35)/(8)+(1)/(64)`

`(t+(1)/(8))^2=(280)/(64)+(1)/(64)`

`(t+(1)/(8))^2=(281)/(64)`
square root both sides, remember to take positive and negative roots

`t+(1)/(8)=(+/-√(281))/(8)`
minus 1/8

`t=(-1+/-√(281))/(8)`


`t=(-1+√(281))/(8)` or
`t=(-1-√(281))/(8)`
the 2nd solution is not valid because that gives us a negative time, before the ball was dropped

so
`t=(-1+√(281))/(8)` is the solution
t≈1.97

1.97 seconds