Velocity of balloon after 10 sec. = `0= 1.25 xx 10`
`" " = 12. 5 m//s`
distance travelled `= (1)/(2) at ^(2) = (1)/(2) (1.25) xx 10^(2)`
`" " = 62.5` m
(i) `h= (u^(2))/(2g)`
` = ((12.5)^(2))/(20) = 7. 8125` m
height from ground = `62.5 + 7.8125 = 70.31`m
(ii) `t_(OA) = (u)/(g) = (12. 5)/(10) = 1.25 sec`.
`t_(AB) = sqrt((2h_(AB))/(g)) = 3.75 sec`.
Total time = 5 sec.