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answer to Q 2

let v be the speed after time t .............as we know there is no force in horizontal direction in projectile motion so ......horizontal component of paticle velocity will always be the same

so u cosa = v cosb

now verticlal component of particle velocity after t time is

vsinb= u sina - gt



use the above two equations to get the answer by eliminating v

.......in above equations a= alpha and b =beta

@giridharg

this equation Sn=u+a(n-1\2) is dimensionaly correct as Sn denotes the distance travel in nth second .............which automatically means distance per (nth)second .........so Sn has a dimension of speed.....