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.

Options

A. `("gt")/(2sin(alpha-beta))`
B. `("gt"cosbeta)/(2sin(alpha-beta))`
C. `(sin(alpha-beta))/(2"gt")`
D. `(2sin(alpha-beta))/("gt"cosbeta)`

Answer

B

Explanation

b. `y/x = tan beta`
`rArr (usin alphat - 1/2 "gt"^2)/(u cos alphat) = tanbeta`
or `usin alpha-tan betaucosalpha = ("gt")/2 or u = (gtcosbeta)/(2sin(alpha-beta))`.
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