(d) When stone travels horizontally then it must be at the maximum height.
So, `2=(u sin theta)/g`
`impliesu sin theta=20`……….(i)
Also, `tan 45^(@)=(u sin theta-g(1))/(u cos theta)`
`implies u cos theta=20-10`
`implies u cos theta =10`…………(ii)
Squaring of Eqs. (i) and (ii) and adding we get
`u=10sqrt(5)ms^(-1)` and `tan theta=2`
`implies theta=tan^(-1)(2)`