Question

plz answer this question

Answer 1

$<b>Given that$
speed of balloon = 10m/s
g = -10m/s^2

Now as the stone is above the balloon then speed of balloon = initial velocity of stone when it starts to fall

then
u of stone = 10 m/s


as we know that
-H = ut +1/2×g×t^2

or -390 = 10t - 5t^2
or - 78 = 2t - t^2

or t^2 -2t -78 = 0

$or \:t = \frac{2 + \sqrt{ {2}^{2} - 4(1)( - 78) } }{2} \\ \\ = \frac{2 + \sqrt{4 + 312} }{2} \\ \\ = \frac{2 + \sqrt{316} }{2} \\ \\ = \frac{2 + 17.8}{2} \\ \\ = \frac{19.8}{2} \\ \\ = 9.9sec$
$\orange{\boxed{\green{Hope\: it \:helps\: you}}}$

Answer 2

$\boxed{\boxed{\boxed{\bold{\red{HEY!\: Here's\: your\: solution}}}}}$
______________________________

$\bold{\green{Please\: refer\: to\: the\: attachment\: for \: the\: solution}}$

$\boxed{\bold{\pink{Your\: answer \: is \: 8.8\: sec\:(approx)}}}$
______________________________

$\bold{\blue{Hope\: the\: answer\: helps\: you}}$