Correct Answer - `75 ms^(-1), (437.5 +- 62.5 sqrt(21))m`
`-25 m//s` After 5 sec
height of balloon `= 25 xx 5 = 125 m`
(i) Minimum speed
`125 = ((u -25)^(2))/(2g) rArr (u -25)^(2)=2500`,
`u-25 =50 , u = 75 m//s`
(ii) `u = 2 xx 75 = 150 m//s`
`125 = (150 - 25)t - 5 t^(2)`
`125 = 125 t - 5t^(2) rArr t^(2) - 25 t + 25 = 0`.