Question

A stone projected at an angle of `60^@` from the ground level strikes at an angle of `30^@` on the roof of a building of height `h`. Then the speed of projection of the stone is:
A. `sqrt(2gh)`
B. `sqrt(6gh)`
C. `sqrt(3gh)`
D. `sqrt(gh)`

Answer 1

Correct Answer - C
Let initial and final speeds of stone be `u` and `v`.
`:. V^(2)=u^(2)-2gh` …….`(1)`
and `v cos 30^(@)=u cos 60^(@)` ……..`(2)`
solving 1 and 2 we get `u=sqrt(3gh)`