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
$(t+\frac{1}{8})^2=\frac{35}{8}+\frac{1}{64}$
$(t+\frac{1}{8})^2=\frac{280}{64}+\frac{1}{64}$
$(t+\frac{1}{8})^2=\frac{281}{64}$
square root both sides, remember to take positive and negative roots
$t+\frac{1}{8}=\frac{+/-\sqrt{281}}{8}$
minus 1/8
$t=\frac{-1+/-\sqrt{281}}{8}$

$t=\frac{-1+\sqrt{281}}{8}$ or $t=\frac{-1-\sqrt{281}}{8}$
the 2nd solution is not valid because that gives us a negative time, before the ball was dropped

so $t=\frac{-1+\sqrt{281}}{8}$ is the solution
t≈1.97

1.97 seconds