question_answer

A particle is projected at an angle of elevation \[\alpha \] and after t seconds it appears to have an angle of elevation \[\beta \] as seen from point of projection. The initial velocity will be

A) \[\frac{gt}{2\sin \left( \alpha -\beta  \right)}\]

B)        \[\frac{gt\,\cos \beta }{2\sin \left( \alpha -\beta  \right)}\]

C) \[\frac{\sin \left( \alpha -\beta  \right)}{2gt}\]         

D)        \[\frac{2\sin \left( \alpha -\beta  \right)}{gt\,\cos \beta }\]