A particle is projected at an angle of elevation `alpha` and after t second it appears to have an elevation of `beta` as seen from the point of projection. Find the initial velocity of projection.

Answer

A, B, C

Explanation

Let v is the velocity at time t
Using `v_y = u_y + a_yt `
`:. v sin beta = usin alpha - g t` ………(i)
`v_x = u_x`
`:. v cos beta = u cos alpha …..(ii)`
From Eqs. (i) and (ii), we get
`((ucosalpha)/(cos beta)) sin beta = u sinalpha -g t`
On solving we get,
`u = (g t cosbeta)/(sin (alpha-beta))`.